NASA has been grabbing headlines recently with their potentially game-changing emDrive propulsion system. The emDrive has generated a lot of discussion, and a lot of controversy too. But NASA has a lot more going on than futuristic space travel designs, and one recent test flight showed that the minds at NASA are still working on innovative designs for flight systems that operate in Earth’s atmosphere.
The Greased Lightning 10, or GL10, is a remotely piloted, ten engine aircraft that can take off and land vertically, and then rotate its wings for forward flight. This type of system has been developed before in full size, piloted aircraft like the V22 Osprey, but it’s never been done before in a small, remotely-piloted aircraft. Continue reading “NASAs Ten-Engine Electric Plane”
The image shown here is the last one acquired and transmitted back to Earth by the mission. The image is located within the floor of the 93-kilometer-diameter crater Jokai. The spacecraft struck the planet just north of Shakespeare basin.
The image measures 0.6 miles (1 km) across. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
The planet Mercury has a brand new 52-foot-wide crater. At 3:26 p.m. EDT this afternoon, NASA’s MESSENGER spacecraft bit the Mercurial dust, crashing into the planet’s surface at over 8,700 mph just north of the Shakespeare Basin. Because the impact happened out of sight and communication with the Earth, the MESSENGER team had to wait about 30 minutes after the predicted impact to announce the mission’s end.
NASA predicted that the MESSENGER spacecraft would crash into Mercury this afternoon at 3:26 p.m. EDT near the 30-mile-wide crater Janacek and the large Shakespeare Basin on the opposite side of the planet from Earth. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Even as MESSENGER faced its demise, it continued to take pictures and gather data right up until impact. The first-ever space probe to orbit the Solar System’s innermost planet, MESSENGER has completed 4,103 orbits as of this morning. Not only has it imaged the planet in great detail, but using it seven science instruments, scientists have gathered data on the composition and structure of Mercury’s crust, its geologic history, the nature of its magnetic field and rarefied sodium-calcium atmosphere, and the makeup of its iron core and icy materials near its poles.
Color-coded view of Carnegie Rupes at left with low elevations in blue and high in red. The ridge formed as Mercury’s interior cooled, resulting in the overall shrinking of the planet. Parts of the landscape lapped over other parts as the planet shrunk. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Images show those ubiquitous craters but also features that set its moonlike landscape apart from the Moon including volcanic plains, tectonic landforms that indicate the planet shrank as its interior cooled and mysterious mouse-like nibbles called “hollows”, where surface material may be vaporizing in sunlight leaving behind a network of holes. To learn more about the mission’s “greatest hits”, check out its Top Ten discoveriesor pay a visit to the Gallery.
The rounded depressions, called “hollows”, are a fascinating discovery of MESSENGER’s orbital mission and may have been formed by vaporization of materials in the surface when exposed by the Raditladi impact. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
MESSENGER mission controllers conducted the last of six planned maneuvers on April 24 to raise the spacecraft’s minimum altitude sufficiently to extend orbital operations and further delay the probe’s inevitable impact onto Mercury’s surface, but it’s now out of propellant. Without the ability to counteract the Sun’s gravity, which is slowly pulling the craft closer to Mercury’s surface, the team prepared for the inevitable.
False color images of Mercury taken with MESSENGER’s Mercury Atmosphere and Surface Composition Spectrometer (MASCS) in everything from infrared to ultraviolet light reveal colorful differences in terrain and surface mineralogy. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
The spacecraft actually ran out of propellant a while back, but controllers realized they could re-purpose a stock of helium, originally carried to pressurize the fuel, for a few final blasts to keep it alive and doing science right up to the last minute. During its final hours today, MESSENGER will be shooting and sending back as many new pictures as possible the same way you’d squeeze in one last shot of the Grand Canyon before departing for home. It’s also holding hundreds of older photos in its memory chip and will send as many of those as it can before the final deadline.
Farewell MESSENGER! Artist view of the spacecraft in orbit about Mercury. Credit: NASA
“Operating a spacecraft in orbit about Mercury, where the probe is exposed to punishing heat from the Sun and the planet’s dayside surface as well as the harsh radiation environment of the inner heliosphere (Sun’s sphere of influence), would be challenge enough,” said Principal Investigator Sean Solomon, MESSENGER principal investigator. “But MESSENGER’s mission design, navigation, engineering, and spacecraft operations teams have fought off the relentless action of solar gravity, made the most of every usable gram of propellant, and devised novel ways to modify the spacecraft trajectory never before accomplished in deep space.”
Face northwest starting about 45 minutes after sunset to find Mercury tonight. It’s located about two fists to the lower right of Venus and just 1.5° below the Pleiades star cluster. Use binoculars to see the star cluster more easily. Source: Stellarium
Ground-based telescopes won’t be able to spy MESSENGER’s impact crater because of its small size, but the BepiColombo Mercury probe, due to launch in 2017 and arrive in orbit at Mercury in 2024, should be able to get a glimpse. Speaking of spying, you can see the planet Mercury tonight (and for the next week or two), when it will be easily visible low in the northwestern sky starting about 45 minutes after sundown. The planet coincidentally makes its closest approach to the Pleiades star cluster tonight and tomorrow.
Use the occasion to wish MESSENGER a fond farewell.
Maybe May 1st is a major holiday in your world scheme, or perhaps you see it as the release date of Avengers: Age of Ultron.
We’re approximately mid-way between the March equinox and the June solstice this week, as followers of the Gregorian calendar flip the page tomorrow from April to May. Though astronomical spring began back on March 20th for the northern hemisphere, May 1st is right around the time it starts to feel like spring weather for most of the residents of mid- northern latitudes.
Blame solar insolation, as the Sun transits ever higher in its daily trek towards the June solstice. Sure, the 23 degree 26’ 21” axial tilt of our fair planet is the reason for the season, and the pair of equinoxes and solstices are easily marked… but did you know that there are four other astronomical waypoints along the ecliptic that aren’t so readily defined?
A ‘sidewalk sundial’ in front of the Flandrau observatory in Tucson, Arizona. Credit and copyright: Dave Dickinson
Welcome to the curious world of cross-quarter days. Tomorrow, May 1st is also known as May Day, which is one such holiday. Perhaps, if you’re reading this in the remaining socialist states of China, Cuba or North Korea, you observe May Day as a major communist holiday. True story: back in our Cold Warrior days, May Day usually meant deployment to a forward location to chase Soviet Bear bombers out of friendly air space.
The cycle of four cross quarter days and four quarter (two solstices and two equinoxes) comprise the modern ‘Wheel of the Year’ on the Pagan calendar. The Christian holidays of Easter and Christmas also have their equinoctial and solstice roots.
The other three cross quarter holidays on our modern calendar are: Groundhog Day (February 2nd), Lammas Day (August 1st) and Halloween on October 31st. It’s great to see suburbanites don garb and request treats in a yearly re-enactment of ancient ritual.
But the solstice and equinoctial points aren’t fixed on the Gregorian calendar, but instead drift as we attempt to keep measured time in sync with astronomical time. These midway dates should actually be referred to as ‘cross-quarter tie-in holidays,’ as the actual midpoint between solstice and equinox can be determined in several different ways.
Here are the technical mid-points for 2015:
*Note that Easter in the Catholic Church is defined by the First Council of Nicaea in 325 A.D. as the first Sunday after the First Full Moon after March 21st. It can, therefore, fall anywhere from March 22nd to April 25th. The Eastern Orthodox Church uses the older Julian calendar, meaning the dates of Easter for the two sects of Christianity do not always coincide. Keep in mind, however, that March 21st is only an approximation for the northward equinox, which, in the 20th through 21st century, can fall anywhere from March 19th to March 21st.
Marking the technical midway point in declination simply means noting when the Sun crosses 11 degrees 43’ 10” north or south. Note that these always cluster with a bias towards the equinoxes, as the apparent motion of the Sun is faster in declination as it moves at a steeper angle around these dates. Sol’s motion in declination is shallowest near the solstices, which is why the gain and loss of daylight is least noticeable around these dates.
The true position of the Sun on May 1st. Credit: Stellarium
And the second way we can mark the technical midpoints is strictly in time… but keep in mind, the seasons are not precisely equal in length due to the elliptical orbit of the Earth. Though it may not seem like it, Earth actually reaches perihelion and moves slightly faster around the Sun in early January during the depths of northern hemisphere winter!
And our friend the precession of the equinoxes plays a role as well, moving the two equinoctial points where the ecliptic and the celestial equator intersect once all the way around the sky as the Earth completes one ‘wobble’ every 26,000 years… live out a typical 72 year life span, and the equinoctial points will have moved about one degree, or twice the diameter of a Full Moon.
An Earthbound analemma simulation. Credit: Starry Night Education Software
And you can ‘observe’ the motion of the Sun and trace out the figure 8 shape of the analemma noting the quarter and cross-quarter points by imaging the Sun at the same time of the day once every week or so for a year:
An analemma over Transylvania. Credit and copyright: Pal Varadi Nagy
Note: make sure you stay on local solar time in your yearlong analemma quest… don’t let the archaic vagaries of Daylight Saving Time throw you off by an hour!
A Mars analemma as seen from Opportunity. Credit: NASA/JPL/Cornell/ASU/TAMU
And other planets have extraterrestrial analemmas as well. In the case of Mars, the path of the Sun over the Martian year is actually teardrop-shaped:
However you reckon the springtime mid-point, don’t miss any local ‘May Day-henge’ alignments coming to a horizon near you.
The overview of the New Horizon journey to the binary system of Pluto and Charon. The NASA probe is now surpassing Hubble imagery. (Photo Credit: NASA/New Horizons)
The latest set of images from the long range imager, LORRI, on New Horizons now reveals surface features. At a press conference today, exhilarated NASA scientists discussed what the images are now suggesting. (Photo Credit: NASA/New Horizons)
Today, a trio of NASA scientists expressed their exhilaration with the set of new Pluto images released by the New Horizons team. “Land Ho” exclaimed Dr. Alan Stern as he first tried to explain where they are on their long journey. Nearly 500 years ago, not even Magellan on a three year journey to circumnavigate the Earth waited so long. A ten year journey is beginning to reveal fascinating new details of the dwarf planet Pluto, once the ninth planet of our Solar System. The latest images show surface features on Pluto suggesting polar caps.
A team effort that Dr. Weaver said called upon leading experts to resolve these newest details of Pluto’s surface. The inset at left shows schematically the geographic relationship of the two bodies as they orbit each other. The inset at right shows surface details at 3x maximum resolution. (Photo Credit: NASA/New Horizons)
The NASA press conference took place this afternoon, anchored by Dr. John Grunsfeld, Associate Administrator for the Science Mission Directorate who quickly turned over the discussion to the project scientist of the New Horizons mission, Dr. Alan Stern from the Southwest Research Institute of San Antonio, Texas. Grunsfeld began by stating NASA’s mission – “to explore, discover and inspire” and added that New Horizons is certainly executing these prime objectives.
The overview of the New Horizon journey to the binary system, Pluto and Charon, and beyond. The NASA probe is now surpassing Hubble imagery. (Photo Credit: NASA/New Horizons)
Alan Stern started off by expressing his excitement with the latest results from the long range telescope on board New Horizons, LORRI, but emphasized he represents a team effort, the culmination of decades of work.
With just 11 weeks remaining and now 98% of the way to Pluto, the latest set of images from LORRI have now revealed details better than the best that was previously attainable – from the Hubble Space Telescope. Most incredible are indications of polar caps on the dwarf planet Pluto.
Until now, the Hubble space telescope had shown tantalizing but mottled features of the surface of Pluto (Photo Credit: NASA)
Dr. Stern, stated that the 25th Anniversay of the Hubble mission has also functioned as a segue to what is about to unfold from New Horizons. Until now, the best images of Pluto’s surface had been wrestled out of images from Hubble with computer processing. Yet, at the present distance New Horizons remains, his team is still relying on image processing to reveal these first surface details.
The gravitational tug of war of the unique binary system has forced both small bodies to forever face each other, similar to how our Moon always faces the Earth. (Photo Credit: NASA/New Horizons)
Dr. Stern stated how remarkable the Pluto-Charon system is. The earlier set of LORRI images from 2014 had shown the gravitational dance of the two small bodies. He stated that they are truly a binary system and a type we have never explored before. Pluto-Charon is a dual synchronous, tidally locked system. Dr. Stern explained that the Earth, close-in to the Sun, and their space probe New Horizons, now on its final approach, is viewing the sunlit side of Pluto and Charon.
The system is tipped over relative to its orbital plane around the Sun. Dr. Stern stated, “it is like watching Pluto rotate on a spit.” He said that we are nearly seeing it face on; similar to an observer hovering far above the Earth’s polar cap and looking down upon the Earth-Moon system. The orbits of the two bodies, as seen in the LORRI image sequence (animations, above), appear elliptical (oval), however, due to the extreme and final state of this binary system, the orbits are perfect circles; the eccentricities are zero! New Horizons is just approaching slightly off center.
Images of the New Horion space probe shows its compactness, necessarily to minimize weight, volume, power demands and achieve the high velocity necessary to reach Pluto in nine years. Af left the instruments are shown included the long range imager, LORRI. (Photo Credit: NASA/New Horizons)
Dr. Stern continued and explained how this latest set is now showing surface features on Pluto. The features “are suggesting the presence of polar caps”, however he also emphasized that it remains only suggestive until New Horizons can deliver more details, that is, higher resolution, color imagery from the Ralph imager and spectroscopic data (Ralph and Alice imaging spectrometers) to reveal composition. Dr. Stern turned over the press conference to Dr. Hal Weaver of John Hopkins’ Applied Physics Laboratory, the lead scientist for the LORRI instrument.
LORRI, the Long Range Reconnaissance Imager, shown through details of a schematic. (Credit: NASA/New Horizons)
LORRI as Dr. Weaver explained is a state-of-the-art instrument. A fixed focus telescopic camera, functional from room temp down to 180 degees Fahrenheit below zero and utilizes an 8 inch primary mirror. The optical quality is extraordinary but the light gathering power is the same as one has in an amateur 8 inch telescope such as offered by Meade or Celestron. Still further, Dr. Weaver stated that LORRI is also extremely efficient and ligthweight, using less than 5 watts of power and weighing less than 20 lbs.
New York City’s Manhattan is shown as an example of the resolving power the Ralph multi-spectral imager will have at closest approach to Pluto and Charon (Photo Credit: NASA/New Horizons)
Dr. Weaver explained how the raw images from LORRI are presently little more than blotches of light, unspectacular at first glance, but with image processing, the details discussed today are revealed. The New Horizons team employed world-class experts in the technique of Image Deconvolution. It was again Hubble that spawned “a cottage industry”, over 20 years ago, including one expert – Todd Lauer of the National Optical Astronomy Observatory. Lauer and others took on the challenge of extracting quality imagery from the Hubble space telescope as it struggled with the astigmatism accidentally built into its optical system. A NASA Space Shuttle mission delivered and inserted a corrective lens into Hubble which has made its 25 years of service possible.
Without the imaging processing technique of deconvolution, the latest images of Pluto are mere blotches. Dr. Weaver credited experts born from the Hubble astigmatism from 20 years ago. (Photo Credit: NASA/New Horizons)
And the New Horizons’ processed images are now slightly better than Hubble and will just get much better. From the Q&A with the press. Weaver explained that while the images show more detail, Earth-based and Hubble images remain more light sensitive. Hubble sets an upper limit to the size of any remaining moons to be discovered. Weaver stated that by June, New Horizons’ LORRI will exceed the light sensitivity limits of Hubble. If there are more moons to be found, June will be the month.
An artist’s illustration of Pluto. With a tenuous atmosphere that has so far defied explanations, New Horizons is altogether revealing a light red – peach – colored surface but with large contrasting areas of white and dark red. (Illust. Credit: NASA/New Horizons)
Through the Q&A, Dr. Stern stated that an extraordinary aspect of Pluto’s atmosphere is that the planet’s atmosphere has continued to expand despite having passed a point in its orbit at which it should be freezing and condensing onto its surface. The atmosphere expanded 200 to 300% in the last decade. With the limited observations, Stern and other Pluto experts surmise that there is a lag in the climate akin to how our hottest months lag the beginning of Summer by a couple of months. Perhaps, a latent heat stored up in the near surface has continued to vaporize frozen gases thus building up the atmosphere more than first expected.
The composition of the dwarf planet’s surface was discussed. Most evident in Earth-based spectroscopy is that there is molecular nitrogen, carbon monoxide and methane. Stern stated they these species of molecules could explain the bright and dark spots of the surface. However, he emphasized that Pluto is composed of 70% rock by mass and the remaining is ice. Charon stands in remarkable contrast to Pluto. Chraon has primarily water and ammonia hydrates on its surface; no detectable atmosphere (so far). Charon’s appearance is much more uniform and bland. Altogether, Stern said that experts call this the Pluto-Charon dichotomy.
The present approach at 60 million miles to Pluto is just the beginning of the story of New Horizons’ study of the primary targets. This press conference illustration explains near-term plans. (Illust. Credit: NASA/New Horizons)
Dr. Stern near the end of the press conference restated that this is truly “my meet Pluto moment.” New Horizons is like a plane on its final approach to touchdown but New Horizons cannot slow down. There are no retro-rockets, no propulsion onboard that can slow down the probe on its trek to escape the gravity of the Sun. The probe will join the Pioneer and Voyager space probes as the only Human-made objects to leave the Solar System. With its final approach, with every day, Pluto and Charon closes in as Dr. Stern and Dr. Weaver explained, Pluto’s image will fill the full breadth of the imaging detector. Details on its surface will be equivalent to high resolution images of New York’s Manhattan (figure, above) showing details such as the ponds in Central Park.
To continue following the latest release of images from New Horizons go to http://www.nasa.gov/newhorizons/lorri-gallery.
A lucky capture of a 2013 Lyrid meteor. Image credit and copyright: John Chumack
April showers bring May flowers, and this month also brings a shower of the celestial variety, as the Lyrid meteors peak this week.
And the good news is, 2015 should be a favorable year for the first major meteor shower of the Spring season for the northern hemisphere. The peak for the shower in 2015 is predicted to arrive just after midnight Universal Time on Thursday April 23rd, which is 8:00 PM EDT on the evening of Wednesday April 22nd. This favors European longitudes right around the key time, though North America could be in for a decent show as well. Remember, meteor showers don’t read forecasts, and the actual peak can always arrive early or late. We plan to start watching tonight and into Wednesday and Thursday morning as well. April also sees a extremely variable level of cloud cover over the northern hemisphere, another reason to start your meteor vigil early on if skies are clear.
The radiant for the 2015 Lyrids as seen from 40 degrees north latitude at local midnight. Credit: Stellarium.
Another favorable factor this year is the phase of the Moon, which is only a slender 20% illuminated waxing crescent on Wednesday night. This means that it will have set well before local midnight when the action begins.
The source of the Lyrid meteors is Comet C/1861 G1 Thatcher, which is on a 415 year orbit and is expected to come back around again in 2276 A.D. 1861 actually sported two great comets, the other being C/1861 J1, also known as the Great Comet of 1861.
The orientation of the Sun, Moon, and the Lyrid radiant at the expected peak of the shower at 24UT/20EDT April 22nd. credit: Stellarium
The Lyrids typically exhibit an ideal Zenithal Hourly Rate (ZHR) of 15-20 per hour, though this shower has been known to produce moderate outbursts from time to time. In 1803 and 1922, the Lyrids produced a ZHR of 100 per hour, and in recent times, we had an outburst of 250 per hour back in 1982. Researchers have tried over the years to tease out a periodicity for Lyrid outbursts, which seem erratic at best. In recent years, the Lyrids hit a ZHR of 20 (2011), 25 (2012), 22 (2013), and 16 last year in 2014.
Keep in mind, we say that the ZHR is an ideal rate, or what you could expect from the meteor shower with the radiant directly overhead under dark skies: expect the actual number of meteors observed during any shower to be significantly less.
A 2014 Lyrid fireball. Credit: The UK Meteor Network
The radiant for the Lyrids actually sits a few degrees east of the bright star Vega across the Lyra border in the constellation Hercules. They should, in fact, be named the Herculids! In mid-April, the radiant for the April Lyrids has already risen well above the northeastern horizon as seen from latitude 40 degrees north at 10 PM local, and is roughly overhead by 4 AM local. Several other minor showers are also active around late April, including the Pi Puppids (April 24th), the Eta Aquarids (May 6th), and the Eta Lyrids (May 9th). The constellation of the Lyre also lends its name to the June Lyrids peaking around June 6th.
The April Lyrids are intersecting the Earth’s orbit at a high 80 degree angle at a swift velocity of 49 kilometres per second. About a quarter of the Lyrid meteors are fireballs, leaving bright, persistent smoke trains. It’s a good idea to keep a set of binoculars handy to study these lingering smoke trails post-passage.
The Lyrids also have the distinction of having the longest recorded history of any known meteor shower. Chinese chronicles indicate that “stars dropped down like rain,” on a late Spring night in 687 BC.
Observing a meteor shower requires nothing more than a set of working ‘Mark-1 eyeballs’ and patience. The International Meteor Organization always welcomes reports of meteor counts from observers worldwide to build an accurate picture of evolving meteor debris streams. You can even hear meteor ‘pings’ via FM radio.
Expect the rate to pick up past local midnight, as the Earth plows headlong into the oncoming meteor stream. Remember, the front of the car gets the love bugs, an apt analogy for any Florida resident in mid-April.
A composite view of the 2012 Lyrids plus sporadic meteors. Credit: NASA/MSFC/Danielle Moser
Catching a photograph of a Lyrid or any meteor is as simple as plopping a DSLR down on a tripod and doing a series of 30 second to several minute long time exposures. Use the widest field of view possible, and aim the camera off at about a 45 degree angle from the radiant to catch the meteors sidelong in profile. Be sure to take a series of test shots to get the ISO/f-stop combination set for the local sky conditions.
Don’t miss the 2015 Lyrids, possibly the first good meteor shower of the year!
Newly found asteroid 2015 HD1 will pay a close visit to Earth overnight, zipping by at just 45,600 miles at 3:11 a.m. Tuesday morning. Credit: Gianluca Masi
If you wake up in the middle of the night with weird dreams about flying asteroids, I wouldn’t be surprised. Around 3 a.m. (CDT) tomorrow morning April 21, a 50-foot-wide asteroid will hurdle just 0.2 lunar distances or 45,600 miles over your bed.
The Mt. Lemmon Survey, based in Tucson, Arizona, snagged the space rock Saturday. 2015 HD1 is about as big as a full grown T-rex through not nearly as scary, since it will safely miss Earth … but not by much.
Artist view of a small asteroid passing near Earth. Credit: NASA
Geostationary satellites, used for global communications, weather forecasting and satellite TV, are parked in orbits about 22,300 miles above the Earth. 2015 HD1 will zip by at just twice that distance, putting it in a more select group of extremely close-approaching objects. Yet given its small size, even if it were to collide with Earth, this dino-sized rock would probably break up into a shower of meteorites.
Lucky for all of us, astronomers conducting photographic surveys like the one at Mt. Lemmon rake the skies every clear night, turning up a dozen or more generally small, Earth-approaching asteroids every month. None yet has been found on a collision course with Earth, but many pass within a few lunar distances.
A common misunderstanding about approaching asteroids concerns Earth’s gravity. While our planet has plenty of gravitational pull, it’s no match for speedy asteroids. We can’t “pull” them in like some tractor beam.
Because they’re moving at miles per second velocities, they have lots of angular momentum (desire to keep moving in the direction they’re headed). Only asteroids headed directly for us have any hope of striking our atmosphere and potentially leaving fragments behind as meteorites.
Still, both Earth and asteroid interact. Close-approaching asteroids often will have their orbits altered by Earth’s gravity. They come in in one direction and leave on a slightly different one after Earth weighs in (literally!)
All the known asteroids orbiting the Sun – in 3D
Moving rapidly across the constellations Hydra, Antlia and Puppis tomorrow morning, 2015 HD1 is expected to reach climb briefly to magnitude +13.2. That’s faint, but with a good map, amateur astronomers with 8-inch or larger telescopes will see it move in real time across the sky like a slow satellite. To create a map, you’ll need sky-charting software like MegaStar, The Sky or Starry Night and these orbital elements.
Maximum brightness and visibility occurs between about 1 and 3 a.m CDT (6-8 UT) for observers in low northern or southern latitudes. From the West Coast, the asteroid will be low in the southwestern sky around 10 p.m. local time. Hawaiian skywatchers will get the brightest views with the asteroid highest in the sky around 9 p.m. local time. IF you live in the eastern two-thirds of the U.S., it’s either too far south or will have set by the time it’s bright enough to see.
No worries. Italian astronomer Gianluca Masi will once again fire up his telescope to provide live views of 2015 HD1 on his Virtual Telescope Project websitetoday April 20 starting at 4 p.m. CDT (21:00 UT). So if you like, you can get a gander after all.
This is a false-color image of the mid-infrared emission from the Great Galaxy in Andromeda, as seen by Nasa's WISE space telescope. The orange color represents emission from the heat of stars forming in the galaxy's spiral arms. The G-HAT team used images such as these to search 100,000 nearby galaxies for unusually large amounts of this mid-infrared emission that might arise from alien civilizations.
Credit: NASA/JPL-Caltech/WISE Team
Beam us up, Scotty. There’s no signs of intelligent life out there. At least, no obvious signs, according to a recent survey performed by researchers at Penn State University. After reviewing data taken by the NASA Wide-field Infrared Survey Explorer (WISE) space telescope of over 100,000 galaxies, there appears to be little evidence that advanced, spacefaring civilizations exist in any of them.
First deployed in 2009, the WISE mission has been able to identify thousands of asteroids in our solar system and previously undiscovered star clusters in our galaxy. However, Jason T. Wright, an assistant professor of astronomy and astrophysics at the Center for Exoplanets and Habitable Worlds at Penn State University, conceived of and initiated a new field of research – using the infrared data to assist in the search for signs of extra-terrestrial civilizations.
And while their first look did not yield much in the way of results, it is an exciting new area of research and provides some very useful information on one of the greatest questions ever asked: are we alone in the universe?
“The idea behind our research is that, if an entire galaxy had been colonized by an advanced spacefaring civilization, the energy produced by that civilization’s technologies would be detectable in mid-infrared wavelengths,” said Wright, “exactly the radiation that the WISE satellite was designed to detect for other astronomical purposes.”
This logic is in keeping with the theories of Russian astronomer Nikolai Kardashev and theoretical physicist Freeman Dyson. In 1964, Kardashev proposed that a civilization’s level of technological advancement could be measured based on the amount of energy that civilization is able to utilize.
Freemon Dyson theorized that eventually, a civilization would be able to enclose its star with a megastructure that would to capture and utilize its energy. Credit: sentientdevelopments.com
To characterize the level of extra-terrestrial development, Kardashev developed a three category system – Type I, II, and III civilizations – known as the “Kardashev Scale”. A Type I civilization uses all available resources on its home planet, while a Type II is able to harness all the energy of its star. Type III civilizations are those that are advanced enough to harness the energy of their entire galaxy.
Similarly, Dyson proposed in 1960 that advanced alien civilizations beyond Earth could be detected by the telltale evidence of their mid-infrared emissions. Believing that a sufficiently advanced civilization would be able to enclose their parent star, he believed it would be possible to search for extraterrestrials by looking for large objects radiating in the infrared range of the electromagnetic spectrum.
These thoughts were expressed in a short paper submitted to the journal Science, entitled “Search for Artificial Stellar Sources of Infrared Radiation“. In it, Dyson proposed that an advanced species would use artificial structures – now referred to as “Dyson Spheres” (though he used the term “shell” in his paper) – to intercept electromagnetic radiation with wavelengths from visible light downwards and radiating waste heat outwards as infrared radiation.
“Whether an advanced spacefaring civilization uses the large amounts of energy from its galaxy’s stars to power computers, space flight, communication, or something we can’t yet imagine, fundamental thermodynamics tells us that this energy must be radiated away as heat in the mid-infrared wavelengths,” said Wright. “This same basic physics causes your computer to radiate heat while it is turned on.”
The Wide-field Infrared Survey Explorer (WISE) scans the entire sky in infrared light, picking up the glow of hundreds of millions of objects and producing millions of images. Credit: NASA/JPL-Caltech
However, it was not until space-based telescopes like WISE were deployed that it became possible to make sensitive measurements of this radiation. WISE is one of three infrared missions currently in space, the other two being NASA’s Spitzer Space Telescope and the Herschel Space Observatory – a European Space Agency mission with important NASA participation.
WISE is different from these missions in that it surveys the entire sky and is designed to cast a net wide enough to catch all sorts of previously unseen cosmic interests. And there are few things more interesting than the prospect of advanced alien civilizations!
To search for them, Roger Griffith – a postbaccalaureate researcher at Penn State and the lead author of the paper – and colleagues scoured the entries in the WISE satellites database looking for evidence of a galaxy that was emitting too much mid-infrared radiation. He and his team then individually examined and categorized 100,000 of the most promising galaxy images.
And while they didn’t find any obvious signs of a Type II civilization or Dyson Spheres in any of them, they did find around 50 candidates that showed unusually high levels of mid-infrared radiation. The next step will be to confirm whether or not these signs are due to natural astronomical processes, or could be an indication of a highly advanced civilization tapping their parent star for energy.
WISE will take images of the most luminous galaxies in the universe, such as the “Cigar” galaxy shown here – taken by NASA’s Spitzer Space Telescope. Credit: NASA/JPL-Caltech/Steward Observatory
In any case, the team’s findings were quite interesting and broke new ground in what is sure to be an ongoing area of research. The only previous study, according to the G-HAT team, surveyed only about 100 galaxies, and was unable to examine them in the infrared to see how much heat they emitted. What’s more, the research may help shed some light on the burning questions about the very existence of intelligent, extra-terrestrial life in our universe.
“Our results mean that, out of the 100,000 galaxies that WISE could see in sufficient detail, none of them is widely populated by an alien civilization using most of the starlight in its galaxy for its own purposes,” said Wright. “That’s interesting because these galaxies are billions of years old, which should have been plenty of time for them to have been filled with alien civilizations, if they exist. Either they don’t exist, or they don’t yet use enough energy for us to recognize them.”
Alas, it seems we are no closer to resolving the Fermi Paradox. But for the first time, it seems that investigations into the matter are moving beyond theoretical arguments. And given time, and further refinements in our detection methods, who knows what we might find lurking out there? The universe is very, very big place, after all.
The research team’s first research paper about their Glimpsing Heat from Alien Technologies Survey (G-HAT) survey appeared in the Astrophysical Journal Supplement Series on April 15, 2015.
A day-old Moon floats over the Spirit Mountain ski hill in Duluth, Minn. this past January. Credit: Bob King
16th century Spanish explorer Juan Ponce de León looked and looked but never did find the Fountain of Youth, a spring rumored to restore one’s youth if you bathed or drank from its waters. If he had, I might have interviewed him for this story.
Sunday night, another symbol of youth beckons skywatchers the world over. A fresh-faced, day-young crescent Moon will hang in the western sky in the company of the planets Mars and Mercury. While I can’t promise a wrinkle-free life, sighting it may send a tingle down your spine reminding you of why you fell in love with astronomy in the first place.
Look low in the west-northwest sky Sunday evening April 19 to spot the day-old crescent Moon alongside Mars and returning Mercury. Brilliant Venus will help you get oriented. This map shows the sky around 40 minutes after sunset but you can start as early as 30 minutes especially if you’re using binoculars. Source: Stellarium
The Moon reaches New Moon phase on Saturday, April 18 during the early afternoon for North and South America. By sunset Sunday, the fragile crescent will be about 29 hours old as seen from the East Coast, 30 for the Midwest, 31 for the mountain states and 32 hours for the West Coast. Depending on where you live, the Moon will hover some 5-7° (three fingers held at arm’s length) above the northwestern horizon 40 minutes after sunset. To make sure you see it, find a location with a wide-open view to the west-northwest.
Earthshine gets easier to see as the Moon moves further from the Sun and the crescent fills out a bit. Our planet provides enough light to spot some of the larger craters. Credit: Bob King
While the crescent is illuminated by direct sunlight, you’ll also see the full outline of the Moon thanks to earthshine. Sunlight reflected off Earth’s globe faintly illuminates the portion of the Moon not lit by the Sun. Because it’s twice-reflected, the light looks more like twilight. Ghostly. Binoculars will help you see it best.
Now that you’ve found the dainty crescent, slide your eyes (or binoculars) to the right. That pinpoint of light just a few degrees away is Mars, a planet that’s lingered in the evening sky longer than you’ve promised to clean out the garage. The Red Planet shone brightly at opposition last April but has since faded and will soon be in conjunction with the Sun. Look for it to return bigger and brighter next May when it’s once again at opposition.
Diagram showing Mercury’s position and approximate altitude above the horizon during the current apparition. Also shown are the planet’s changing phases, which are visible in a telescope. Credit: Stellarium, Bob King
To complete the challenge, you’ll have to look even lower in the west to spot Mercury. Although brighter than Vega, it’s only 3° high 40 minutes after sunset Sunday. Its low altitude makes it Mercury is only just returning to the evening sky in what will become its best appearance at dusk for northern hemisphere skywatchers in 2015.
As an inner planet, Mercury goes through phases just like Venus and the Moon. We see it morph from crescent to “full moon” as its angle to the Sun changes during its revolution of the Sun. Credit: ESO
Right now, because of altitude, the planet’s a test of your sky and observing chops, but let the Moon be your guide on Sunday and you might be surprised. In the next couple weeks, Mercury vaults from the horizon, becoming easier and easier to see. Greatest elongation east of the Sun occurs on the evening of May 6. Although the planet will be highest at dusk on that date, it will have faded from magnitude -0.5 to +1.2. By the time it leaves the scene in late May, it will become very tricky to spot at magnitude +3.5.
Mercury’s a bit different from Venus, which is brighter in its crescent phase and faintest at “full”. Mercury’s considerably smaller than Venus and farther from the Earth, causing it to appear brightest around full phase and faintest when a crescent, even though both planets are largest and closest to us when seen as crescents.
Not to be outdone by the Venus-Pleiades conjunction earlier this month, Mercury passes a few degrees south of the star cluster on April 29. The map shows the sky facing northwest about 50 minutes after sunset. Source: Stellarium
Venus makes up for its dwindling girth by its size and close proximity to Earth. It also doesn’t hurt that it’s covered in highly reflective clouds. Venus reflects about 70% of the light it receives from the Sun; Mercury’s a dark world and gives back just 7%. That’s dingier than the asphalt-toned Moon!
Good luck in your mercurial quest. We’d love to hear your personal stories of the hunt — just click on Comments.
Dawn's framing camera took these images of Ceres on April 10, 2015 which were combined into a short animation. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Brand new images taken on April 10 by NASA’s Dawn probe show the dwarf planet from high above its north pole. Photographed at a distance of just 21,000 miles (33,000 km) — less than 1/10 the Earth-moon distance — they’re our sharpest views to date. The crispness combined with the low-angled sunlight gives Ceres a stark, lunar-like appearance.
Artist’s concept of Dawn above Ceres around the time it was captured into orbit by the dwarf planet in early March. Since its arrival, the spacecraft turned around to point the blue glow of its ion engine in the opposite direction. Because it’s been facing the Sun while lowering its orbit, the new images of Ceres show it as a crescent. Credit: NASA/JPL
Images will only get better. Dawn arrived at Ceres on March 6 and immediately got to work using its ion thrusters in conjunction with the dwarf planet’s gravity to gradually lower itself into a circular orbit. Once the spacecraft settles into its first science orbit on April 23 at a distance of 8,400 miles from the surface, it will begin taking a hard look at this cratered mini-planet. A little more than two weeks later, the probe will spiral down for an even closer view on May 9.
The map is an enhanced color view that offers an expanded range of the colors visible to human eyes. Pictures were taken using blue, green and infrared filters and combined. Scientists use this technique to highlight subtle color differences across Ceres, which can provide insights into the physical properties and composition of the surface. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/ID
Dawn’s gravity spiral continues throughout the summer and fall until the probe tiptoes down to just 233 miles (375 km) altitude in late November. From there it will deploy its Gamma Ray and Neutron Detector (GRaND) to map the elements composing Ceres’ surface rocks. We’re in for a great ride!
Simulated Ceres rotation by Tom Ruen using the new color map
Meanwhile, scientists have assembled images taken by Dawn through blue, green and infrared filters to create a new color-enhanced map of the dwarf planet. The variety of landforms in conjunction with the color variations hint that Ceres was once an active body or one with the means to resurface itself from within. Mechanisms might involve internal heating and / or movement of water or ice.
Pictures from Dawn’s VIR instrument highlight two regions on Ceres containing bright spots. The top images show a region scientists labeled “1” and the bottom images show the region labeled “5,” which show the Ceres’ brightest pair of spots. Region 1 is cooler than the rest of Ceres’ surface, but region 5 appears to be located in a region that is similar in temperature to its surroundings. Credit: NASA/JPL-Caltech/UCLA/ASI/INAF
There are still no new close-ups of the pair of enigmatic white spots taunting us from inside that 57-mile-wide crater. But there is a bit of news. Dawn’s visible and infrared mapping spectrometer or VIR has already examined Ceres in visible and infrared or thermal light. Data from VIR indicate that light and darker regions on the dwarf planet have different properties.
A topographic map of Ceres with provisional names given to each quadrangle. Ceres’ craters are named for agricultural gods; other features after world agricultural festivals. Let’s hope the names are made permanent. I mean, you can’t beat Yumyum. Credit: NASA / JPL / UCLA / MPS / DLR / IDA / JohnVV / Emily Lakdawalla
The bright spots are located in a region with a temperature similar to its surroundings. However, a different bright feature appears in a region that’s cooler than the neighboring surface. Exactly what those variations are telling us will hopefully become clear once Dawn returns more detailed images:
“The bright spots continue to fascinate the science team, but we will have to wait until we get closer and are able to resolve them before we can determine their source,” said Chris Russell, principal investigator for the Dawn mission.
There is something about them that intrigues us all. These massive spheres of gas burning intensely from the energy of fusion buried many thousands of kilometers deep within their cores. The stars have been the object of humanity’s wonderment for as far back as we have records. Many of humanity’s religions can be tied to worshiping these celestial candles. For the Egyptians, the sun was representative of the God Ra, who each day vanquished the night and brought light and warmth to the lands. For the Greeks, it was Apollo who drove his flaming chariot across the sky, illuminating the world. Even in Christianity, Jesus can be said to be representative of the sun given the striking characteristics his story holds with ancient astrological beliefs and figures. In fact, many of the ancient beliefs follow a similar path, all of which tie their origins to that of the worship of the sun and stars.
Humanity thrived off of the stars in the night sky because they recognized a correlation in the pattern in which certain star formations (known as constellations) represented specific times in the yearly cycle. One of which meant that it was to become warmer soon, which led to planting food. The other constellations foretold the coming of a
The familiar constellation of Orion. Orion’s Belt can be clearly seen, as well as Betelgeuse (red star in the upper left corner) and Rigel (bright blue star in the lower right corner) Credit: NASA Astronomy Picture of the Day Collection NASA
colder period, so you were able to begin storing food and gathering firewood. Moving forward in humanity’s journey, the stars then became a way to navigate. Sailing by the stars was the way to get around, and we owe our early exploration to our understandings of the constellations. For many of the tens of thousands of years that human eyes have gazed upwards toward the heavens, it wasn’t until relatively recently that we fully began to understand what stars actually were, where they came from, and how they lived and died. This is what we shall discuss in this article. Come with me as we venture deep into the cosmos and witness physics writ large, as I cover how a star is born, lives, and eventually dies.
We begin our journey by traveling out into the universe in search of something special. We are looking for a unique structure where both the right circumstances and ingredients are present. We are looking for what astronomer’s call a Dark Nebula. I’m sure you’ve heard of nebulae before, and have no doubt seen them. Many of the amazing images that the Hubble Space Telescope has obtained are of beautiful gas clouds, glowing amidst the backdrop of billions of stars. Their colors range from deep reds, to vibrant blues, and even some eerie greens. This is not the type of nebula we are in search of though. The nebula we need is dark, opaque, and very, very cold.
You may by wondering to yourself, “Why are we looking for something dark and cold when stars are bright and hot?”
Image of a Dark Nebula Credit: ESO http://www.eso.org/public/images/eso1501a
Indeed, this is something that would appear puzzling at first. Why does something need to be cold first before it can become extremely hot? First, we must cover something elementary about what we call the Interstellar Medium (ISM), or the space between the stars. Space is not empty as its name would imply. Space contains both gas and dust. The gas we are mainly referring to is Hydrogen, the most abundant element in the universe. Since the universe is not uniform (the same density of gas and dust over every cubic meter), there are pockets of space that contain more gas and dust than others. This causes gravity to manipulate these pockets to come together and form what we see as nebulae. Many things go into the making of these different nebulae, but the one that we are looking for, a Dark Nebula, possesses very special properties. Now, let us dive into one of these Dark Nebulae and see what is going on.
As we descend through the outer layers of this nebula, we notice that the temperature of the gas and dust is very low. In some nebulae, the temperatures are very hot. The more particles bump into each other, excited by the absorption and emission of exterior and interior radiation, means higher temperatures. But in this Dark Nebula, the opposite is happening. The temperatures are decreasing the further into the cloud we get. The reason these Dark Nebulae have specific properties that work to create a great stellar nursery has to deal with the basic properties of the nebula and the region type that the cloud exists in, which has some difficult concepts associated with it that I will not fully illustrate here. They include the region where the molecular clouds form which are called Neutral Hydrogen Regions, and the properties of these regions have to deal with electron spin values, along with magnetic field interactions that effect said electrons. The traits that I will cover are what allows for this particular nebula to be ripe for star formation.
Excluding the complex science behind what helps form these nebulae, we can begin to address the first question of why must we get colder to get hotter. The answer comes down to gravity. When particles are heated, or excited, they move faster. A cloud with sufficient energy will contain far too much momentum among each of the dust and gas particles for any type of formations to occur. As in, if dust grains and gas atoms are moving too quickly, they will simply bounce off of one another or just shoot past each other, never achieving any type of bond. Without this interaction, you can never have a star. However, if the temperatures are cold enough, the particles of gas and dust are moving so slow that their mutual gravity will allow for them to start to “stick” together. It is this process that allows for a protostar to begin to form.
Generally what supplies energy to allow for the faster motion of the particles in these molecular clouds is radiation. Of course, there is radiation coming in from all directions at all times in the universe. As we see with other nebulae, they are glowing with energy and stars aren’t being born amid these hot gas clouds. They are being heated by external radiation from other stars and from its own internal heat. How does this Dark Nebula prevent external radiation from heating up the gas in the cloud and causing it to move too fast for gravity to take hold? This is where
Barnard 68 is a large molecular cloud that is so thick, it blocks out the light from stars that we normally would be able to see. Credit: ESO http://www.eso.org/public/images/eso0102a
the opaque nature of these Dark Nebulae comes into play. Opacity is the measure of how much light is able to move through an object. The more material in the object or the thicker the object is, the less light is able to penetrate it. The higher frequency light (Gamma Rays, X-Rays, and UV) and even the visible frequencies are affected more by thick pockets of gas and dust. Only the lower frequency types of light, including Infrared, Microwaves, and Radio Waves, has any success of penetrating gas clouds such as these, and even it is somewhat scattered so that generally they do not contain nearly enough energy to begin to disrupt this precarious process of star formation. Thus, the inner portions of the dark gas clouds are effectively “shielded” from the outside radiation that disrupts other, less opaque nebulae. The less radiation that makes it into the cloud, the lower the temperatures of the gas and dust within it. The colder temperatures means less particle motion within the cloud, which is key for what we will discuss next.
Indeed, as we descend towards the core of this dark molecular cloud, we notice that less and less visible light makes it to our eyes, and with special filters, we can see that this is true of other frequencies of light. As a result, the cloud’s temperature is very low. It is worth noting that the process of star formation takes a very long time, and in the interest of not keeping you reading for hundreds of thousands of years, we shall now fast forward time. In a few thousand years, gravity has pulled in a fair amount of gas and dust from the surrounding molecular cloud, causing it to clump together. Dust and gas particles, still shielded from outside radiation, are free to naturally come together and “stick” at these low temperatures. Eventually, something interesting begins to happen. The mutual gravity of this ever growing ball of gas and dust begins a snowball (or star-ball) effect. The more layers of gas and dust that are coagulated together, the denser the interior of this protostar becomes. This density increases the gravitational force near the protostar, thus pulling more material into it. With every dust grain and hydrogen atom that it accumulates, the pressure in the interior of this ball of gas increases.
If you remember anything from any chemistry class you’ve ever taken, you may recall a very special relationship between pressure and temperature when dealing with a gas. PV=nRT, the Ideal Gas Law, comes to mind. Excluding the constant scalar value ‘n’ and the gas constant R ({8.314 J/mol x K}), and solving for Temperature (T), we get T=PV, which means that the temperature of a gas cloud is directly proportional to pressure. If you increase the pressure, you increase the temperature. The core of this soon-to-be star residing in this Dark Nebula is becoming very dense, and the pressure is skyrocketing. According to what we just calculated, that means that the temperature is also increasing.
Artistic rendition of a star forming within a dark nebula. Credit: NASA/JPL-Caltech/R. Hurt (SSC)
We yet again consider this nebula for the next step. This nebula has a large amount of dust and gas (hence it being opaque), which means it has a lot of material to feed our protostar. It continues to pull in the gas and dust from its surrounding environment and begins heating up. The hydrogen particles in the core of this object are bouncing around so quick that they are releasing energy into the star. The protostar begins to get very hot and is now glowing with radiation (generally Infrared). At this point, gravity is still pulling in more gas and dust which is adding to the pressures exerted deep within the core of this protostar. The gas of the Dark Nebula will continue to collapse in on itself until something important happens. When there is little to nothing left near the star to fall onto its surface, it begins to lose energy (due to it radiating away as light). When this happens, that outward force lessens and gravity starts to contract the star faster. This greatly increases the pressure in the core of this protostar. As the pressure grows, the temperature in the core reaches a value that is crucial for the process that we are witnessing. The protostar’s core has become so dense and hot, that it reaches roughly 10 million Kelvin. To put that into perspective, this temperature is roughly 1700x hotter than the surface of our sun (at around 5800K). Why is 10 million Kelvin so important? Because at that temperature, the thermonuclear fusion of Hydrogen can occur, and once fusion starts, this newborn star “turns on” and bursts to life, sending out vast amounts of energy in all directions.
In the core, it is so hot that the electrons that zip around the hydrogen’s proton nuclei are stripped off (ionized), and all you have are free moving protons. If the temperature isn’t hot enough, these free flying protons (which have positive charges), will simply glance off one another. However, at 10 Million Kelvin, the protons are moving so fast that they can get close enough to allow for the Strong Nuclear Force to take over, and when it does the Hydrogen protons begin slamming into each other with enough force to fuse together, creating Helium atoms and releasing lots of energy in the form of radiation. It’s a chain reaction that can be summed up as 4 Protons yield 1 Helium atom + energy. This fusion is what ignites the star and causes it to “burn”. The energy liberated by this reaction goes into helping other Hydrogen protons fuse and also supplies the energy to keep the star from collapsing in on itself. The energy that is pumping out of this star in all directions all comes from the core, and the subsequent layers of this young star all transmit that heat in their own way (using radiation and convection methods depending upon what type of star has been born).
Newborn stars glow through their parent molecular cloud Credit: ESA/Hubble & NASA Acknowledgement: Judy Schmidt
What we have witnessed now, from the start of our journey when we dove down into that cold Dark Nebula, is the birth of a young, hot star. The nebula protected this star from errant radiation that would have disrupted this process, as well as providing the frigid environment that was needed for gravity to take hold and work its magic. As we witnessed the protostar form, we may also have seen something incredible. If the contents of this nebula are right, such as having a high amount of heavy metals and silicates (left over from the supernovae of previous, more massive stars) what we could begin to see would be planetary formation taking place in the accretion disk of material around the protostar.
Remaining gas and dust in the vicinity of our new star would begin to form dense pockets by the same mechanism of
Artistic rendition of a protoplanet forming within the accretion disk of a protostar Credit: ESO/L. Calçada http://www.eso.org/public/images/eso1310a/
gravity, eventually being able to accrete into protoplanets that will be made up of gas or silicates and metal (or a combination of the two). That being said, planetary formation is still somewhat a mystery to us, as there seems to be things that we cannot explain yet at work. But this model of star system formation seems to work well.
The life of the star isn’t nearly as exciting as its birth or death. We will continue to fast forward the clock and watch this star system evolve. Over a few billion years, the remnants of the Dark Nebula have been blown apart and have also formed other stars like the one we witnessed, and it no longer exists. The planets we saw being formed as the protostar grew begin their billion year dance around their parent star. Maybe on one of these worlds, a world that sits at just the right distance away from the star, liquid water exists. Within that water contains the amino acids that are needed for proteins (all composed of the elements that were left over by previous stellar eruptions). These proteins are able to link together to start to form RNA chains, then DNA chains. Maybe at one point a few billion years after the star has been born, we see a space-faring species launch itself into the cosmos, or perhaps they never achieve this for various reasons and remain planet-bound. Of course this is just speculation for our amusement. However, now we come to the end of our journey that began billions of years ago. The star begins to die.
The Hydrogen in its core is being fused into Helium, which depletes the Hydrogen over time; the star is running out of gas. After many years, the hydrogen fusion process begins to stop, and the star puts out less and less energy. This lack of outward pressure from the fusion process upsets what we call the hydrostatic equilibrium, and allows gravity (which is always trying to crush the star) to win. The star begins to shrink rapidly under its own weight. But, just as we discussed earlier, as the pressure increases, so too does the temperature. All of that Helium that was left over
Inward force of gravity versus the outward pressure of fusion within a star (hydrostatic equilibrium) Credit: NASA
from the billions of years of hydrogen fusion now begins to heat up in the core. Helium fuses at a much hotter temperature than Hydrogen does, which means that the Helium rich core is able to be pressed inward by gravity without fusing (yet). Since fusion isn’t occurring in the Helium core, there is little to no outward force (given off by fusion) to prevent the core from collapsing. This matter becomes much denser, which we now label as degenerate, and is pushing out massive amounts of heat (gravitational energy becoming thermal energy). This causes the remaining Hydrogen that is in subsequent layers above the Helium core to fuse, which causes the star to expand greatly as this Hydrogen shell burns out of control. This makes the star “rebound” and it expands rapidly; the more energetic fusion from the Hydrogen shells outside of the core expanding the diameter of the star greatly. Our star is now a red giant. Some, if not all of the inner planets that we witnessed form will be incinerated and swallowed up by the star that first gave them life. If there happened to be any life on any of those planets that didn’t manage to leave their home world, they would certainly be erased from the universe, never to be known of.
This process of the star running out of fuel (first Hydrogen, then Helium, etc…) will continue for a while. Eventually, the Helium in the core will reach a certain temperature and begin to fuse into Carbon, which will put off the collapse (and death) of the star. The star we are currently watching live and die is an average-sized Main Sequence Star, so its life ends once it is finished fusing Helium into
Different planetary nebulae, all remnants of low mass stars ejecting their outer material as they die Credit: NASA
Carbon. If the star was much larger, this fusion process would proceed until we reached Iron. Iron is the element in which fusion does not take place spontaneously, meaning it requires more energy to fuse it than it gives off after fusion. However, our star will never make it to Iron in its core, and thus it has died after it exhausts its Helium reservoir. When the fusion process finally “turns off” (out of gas), the star slowly begins to cool and the outer layers of the star expand and are ejected into space. Subsequent ejections of stellar material proceed to create what we call a planetary nebula, and all that is left of the once brilliant star we watched spring into existence is now just a ball of dense carbon that will continue to cool for the rest of eternity, possibly crystallizing into diamond.
The death we witnessed just now isn’t the only way a star dies. If a star is sufficiently large enough, its death is much more violent. The star will erupt into the largest explosion in the universe, called a supernova. Depending on many variables, the remnant of the star could end up as a neutron star, or even a black hole. But for most of what we call the average sized Main Sequence Stars, the death that we witnessed will be their fate.
Artistic representation of the material around the supernova 1987A. Supernovae are among the most violent events in the universe Credit: ESO/L. Calçada
Our journey ends with us pondering what we have observed. Seeing just what nature can do given the right circumstances, and watching a cloud of very cold gas and dust turn into something that has the potential to breathe life into the cosmos. Our minds wander back to that species that could have evolved on one of those planets. You think about how they may have gone through phases similar to us. Possibly using the stars as supernatural deities that guided their beliefs for thousands of years, substituting answers in for where their ignorance reigned. These beliefs could possibly turn into religions, still grasping that notion of special selection and magnanimous thought. Would the stars fuel their desire to understand the universe as the stars did for us? Your mind then ponders what our fate will be if we do not attempt to take the next step into the universe. Are we to allow our species to be erased from the cosmos as our star expands in its death? This journey you just made into the heart of a Dark Nebula truly exemplifies what the human mind can do, and shows you just how far we have come even though we are still bound to our solar system. The things you have learned were found by others like you simply asking how things occur and then bringing the full weight of our knowledge of physics to bare. Imagine what we can accomplish if we continue this process; being able to fully achieve our place among the stars.
The vastness of the cosmos awaits us… Credit: NASA (Hubble Deep Field)
