Astronomy Archives

November 27, 2013December 23, 2015 by David Dickinson

ISON Watch: A Post-Perihelion Viewing Guide

ISON: A 2013 pre-perihelion portrait. (Credit and copyright: Efrain Morales/Jaicoa observatory. Used with permission).

“ISON Lives!!!”

“ISON R.I.P…”

Those are just some of the possible headlines that we’ve wrestled with this week, as Comet C/2012 S1 ISON approaches perihelion tomorrow evening. It’s been a rollercoaster ride of a week, and this sungrazing comet promises to keep us guessing right up until the very end.

Comet ISON reaches perihelion on U.S. Thanksgiving Day Thursday, November 28^th at around 18:44 Universal Time/ 1:44 PM Eastern Standard Time. ISON will pass 1.2 million kilometres from the surface of the Sun, just over eight times farther than Comet C/2011 W3 Lovejoy did in 2011, and about 38 times closer to the Sun than Mercury reaches at perihelion.

Comet ISON as seen from Ottawa, Canada on the morning of November 20th. (Credit: Andrew Symes/@FailedProtostar).

Earth-based observers essentially lost sight of ISON in the dawn twilight this past weekend, and there were fears that the comet might’ve disintegrated all together as it was tracked by NASA’s STEREO spacecraft. Troubling reports circulated early this week that emission rates for the comet had dropped while dust production had risen, possibly signaling that fragmentation of the nucleus was imminent. Certainly, this comet is full of surprises, and our observational experience with large sungrazing comets of this sort is pretty meager.

Credit: SOHO — ISON (entering frame, to the right) currently “photobombing” SOHO’s LASCO C3 camera. Credit: NASA/ESA/SOHO.

However, as ISON entered the field of view of the Solar and Heliospheric Observatory’s LASCO C3 camera earlier today it still appeared to have some game left in it. NASA’s Solar Dynamics Observatory will pick up ISON starting at around 17:09UT/12:09 PM EST tomorrow, and track it through its history-making perihelion passage for just over two hours until 19:09UT/2:19PM EST.

And just as with Comet Lovejoy a few years ago, all eyes will be glued to the webcast from NASA’s Solar Dynamics Observatory as ISON rounds the bend towards its date with destiny… don’t miss it!

Note: you can also follow ISON’s current progress as seen from SOHO at their website!

The tracking plan for the Solar Dynamics Observatory on November 28th as ISON passes through perihelion. (Credit: NASA/SDO).

For over the past year since its discovery, pundits have pondered what is now the astronomical question of the approaching hour: just what is ISON going to do post-perihelion? Will it dazzle or fizzle? In this context, ISON has truly become “Schrödinger’s Comet,” both alive and dead in the minds of those who would attempt to divine its fate.

Recent estimates place ISON’s nucleus at between 950 and 1,250 metres in diameter. This is well above the 200 metre size that’s considered the “point of no return” for a comet passing this close to the Sun. But again, another key factor to consider is how well put together the nucleus of the comet is: a lumpy rubble pile may not hold up against the intense heat and the gravitational tug of the Sun!

Current updated light curve for ISON. Be sure to check with NASA's Comet ISON Observing Campaign for the latest updates. (Compiled by Matthew Knight on November 24th, 2013). — Current updated light curve for ISON. Be sure to check with NASA’s Comet ISON Observing Campaign for the latest updates. (Compiled by Matthew Knight on November 24th, 2013).

But what are the current prospects for spotting ISON after its fiery perihelion passage?

If the comet holds together, reasonable estimates put its maximum brightness near perihelion at between magnitudes -3 and -5, in the range of the planet Venus at maximum brilliancy. ISON will, however, only stand 14’ arc minutes from the disk of the Sun (less than half its apparent diameter) at perihelion, and spying it will be a tough feat that should only be attempted by advanced observers.

Note that for observers based at high northern latitudes “north of the 60,” the shallow angle of the ecliptic might just make it possible to spot Comet ISON low in the dawn after perihelion and before sunrise November 29^th:

ISON Perihelion 1730UT Fairbanks — ISON post-perihelion at sunrise on November 29th as seen from Fairbanks, Alaska. (Created using Starry Night Education software.

We’ve managed to see the planet Venus the day of solar conjunction during similar circumstances with the Sun just below the horizon while observing from North Pole, Alaska.

Most northern hemisphere observers may catch first sight of Comet ISON post-perihelion around the morning of December 1^st. Look low to the east, about half an hour before local sunrise. Use binoculars to sweep back and forth on your morning comet dawn patrol. Note that on December 1^st, Saturn, Mercury, and the slim waning crescent Moon will also perch nearby!

Comet ISON will rapidly gain elevation on successive mornings as it heads off to the northeast, but will also rapidly decrease in brightness as well. If current projections hold, ISON will dip back below magnitude 0 just a few days after perihelion, and back below naked eye visibility by late December. Observers may also be able to start picking it up low to the west at dusk by mid-December, but mornings will be your best bet.

ISON path — The path of comet ISON for the first week of December as seen from latitude 30 degrees north. Note: the planets and the Moon are depicted for December 1st. (Created using Stellarium).

Keep in mind, if ISON fizzles, this could become a “death-watch” for the remnants of the comet, as fragments that might only be visible with binoculars or a telescope follow its outward path. If this turns out to be the case, then the best views of the “Comet formerly known as ISON” have already occurred.

Another possible scenario is that the comet might fragment right around perihelion, leaving us with a brief but brilliant “headless comet,” similar to W3 Lovejoy back in late 2011. The forward light scattering angle for any comet is key to visibility, and in this aspect, ISON is just on the grim edge in terms of its potential to enter the annals of “great” comets, such as Comet Ikeya-Seki back in 1965.

ISON will then run nearly parallel to the 16 hour line in right ascension from south to north through the month of December as it crosses the celestial equator, headed for a date with the north celestial pole just past New Years Day, 2014.

Whether as fragments or whole, comets have to obey Sir Isaac and his laws of physics as they trace their elliptical path back out of the solar system. Keep in mind, a comet’s dust tail actually precedes it on its way outbound as the solar wind sweeps past, a counter-intuitive but neat concept we may just get to see in action soon.

Here are some key dates to watch for as ISON makes tracks across the northern hemisphere sky. Passages are noted near stars brighter than +5^th magnitude and closer than one degree except as mentioned:

November 29th through December 15th. — The celestial path of ISON from November 29th to December 15th. (Credit: Starry Night).

December 1st: ISON is grouped with Saturn, Mercury and the slim crescent Moon in the dawn.

December 2nd: Passes near the +4.9 magnitude star Psi Scorpii.

December 3rd: Passes into the constellation Ophiuchus.

December 5th: Passes near the +2.7 magnitude multiple star Yed Prior.

December 6th: Crosses into the constellation Serpens Caput.

December 8th: Crosses from south to north of the celestial equator.

December 15th: Passes into the constellation Hercules and near the +5^th magnitude star Kappa Herculis.

December 17th: The Moon reaches Full, marking the middle of a week with decreased visibility for the comet.

December 19th: Passes into the constellation of Corona Borealis.

December 20th: Passes near the +4.8^th magnitude star Xi Coronae Borealis.

December 22nd: Passes 5 degrees from the globular cluster M13. Photo op!

Dec 16-Jan 8 — The path of Comet ISON from December 16th to January 8th. (Credit: Starry Night).

December 23^rd: Crosses back into the constellation Hercules.

December 24^th: Passes near the +3.9 magnitude star Tau Herculis.

December 26^th: Comet ISON passes closest to Earth at 0.43 A.U. or 64 million kilometres distant, now moving with a maximum apparent motion of nearly 4 degrees a day.

December 26^th: Crosses into the constellation Draco and becomes circumpolar for observers based at latitude 40 north.

December 28^th: Passes the +2.7 magnitude star Aldhibain.

December 29^th: Passes the +4.8 magnitude star 18 Draconis.

December 31^st: Passes the 4.9 magnitude star 15 Draconis.

January 2^nd: Crosses into the constellation Ursa Minor.

January 4th: Crosses briefly back into the constellation Draco.

January 6th: Crosses back into the constellation Ursa Minor.

January 7th: Crosses into Cepheus; passes within 2.5 degrees of Polaris and the North Celestial Pole.

And after what is (hopefully) a brilliant show, ISON will head back out into the depths of the solar system, perhaps never to return. Whatever the case turns out to be, observations of ISON will have produced some first-rate science… and no planets, popes or prophets will have been harmed in the process. And while those in the business of predicting doom will have moved on to the next apocalypse in 2014, the rest of us will have hopefully witnessed a dazzling spectacle from this icy Oort Cloud visitor, as we await the appearance of the next Great Comet.

Enjoy the show!

ISON: "Great Comet" or the "Great Pumpkin?" Photo and gourd-based artwork by author. — ISON: “Great Comet” or “Great Pumpkin?” Photo and gourd-based artwork by author.

– Got question about Comet ISON? Lights in the Dark has answers!

– Be sure to post those amazing post-perihelion pics of Comet ISON on Universe Today’s Flickr page.

November 27, 2013December 23, 2015 by Elizabeth Howell

Anybody Want A Peanut? New Model Shows Tasty Orbital Shapes In Milky Way’s Bulge

Artist's impression of the Milky Way, looking at it edge on. This makes the bulge at the center look like a peanut, astronomers say. Credit: ESO/NASA/JPL-Caltech/M. Kornmesser/R. Hurt.

Remember that 3-D map of the Milky Way that postulated that the center of the galaxy is shaped like a box or peanut? A new math model of the bulge shows that stars in the center of that bulge move in figure-eight orbits (which can also be interpreted as a peanut-shell shape.) Before, previous studies suggested these orbits looked more like bananas.

“The difference is important; astronomers develop theories of star motions to not only understand how the stars in our galaxy are moving today but also how our galaxy formed and evolves,” the Royal Astronomical Society stated.

In the middle of the galaxy, there are a lot of gravitational forces at play due to the sheer number of stars, as well as particles of dust and dark matter, congregating in the area. This makes it harder to model orbits than in more simple situations, such as our own solar system.

This is how a new model envisions it working:

“As the stars go round in their orbits, they also move above or below the plane of the bar. When stars cross the plane they get a little push, like a child on a swing,” the RAS said.

“At the resonance point, which is a point a certain distance from the center of the bar, the timing of the pushes on the stars is such that this effect is strong enough to make the stars at this point move up higher above the plane. (It is like when a child on the swing has been pushed a little every time and eventually is swinging higher.) These stars are pushed out from the edge of the bulge.”

The researchers suppose that the stars would have two “vertical oscillations” in each orbit, but in between the orbits are shaped somewhat like a peanut shell. This “could give rise to the observed shape of the bulge, which is also like a peanut-shell,” RAS stated.

The research (led by Alice Quillen, an astronomy researcher at the University of Rochester) is available in the Monthly Notices of the Royal Astronomical Society, as well as (in preprint version) on Arxiv.

Source: Royal Astronomical Society

November 27, 2013December 23, 2015 by Elizabeth Howell

Kepler May Go Planet-Hunting Again! Infographic Shows How That Would Work

Infographic showing how the Kepler space telescope could continue searching for planets despite two busted reaction wheels. Credit: NASA Ames/W Stenzel

The planet-seeking Kepler space telescope had to stop its primary mission this summer after the failure of a second of its four reaction wheels, the devices that keep it pointing at a spot in the constellation Cygnus. NASA, however, has a backup plan. It’s considering stabilizing the spacecraft using the sun! You can see the details in this infographic.

The plan is still preliminary as it needs testing, and it also needs budgetary approval while NASA is fighting to keep other programs going at the funding levels the agency wants. But if it works, this is what NASA is proposing:

Keep the spacecraft oriented almost parallel to its orbit around the sun.
Gaze at a particular part of the sky for 83 days.
When the sun is close to coming into the telescope, move the spacecraft and do another 83-day observation period.
This would mean the spacecraft will have 4.5 “unique viewing periods” a year, NASA says.

“With the failure of a second reaction wheel, the spacecraft can no longer precisely point at the mission’s original field of view. The culprit is none other than our own sun,” NASA stated in a recent press release.

Artist's conception of the Kepler Space Telescope. Credit: NASA/JPL-Caltech — Artist’s conception of the Kepler Space Telescope. Credit: NASA/JPL-Caltech

“The very body that provides Kepler with its energy needs also pushes the spacecraft around by the pressure exerted when the photons of sunlight strike the spacecraft. Without a third wheel to help counteract the solar pressure, the spacecraft’s ultra-precise pointing capability cannot be controlled in all directions.”

But this could be a way to counteract it. Mission managers put Kepler through a 30-minute test in October where the telescope looked at a spot in the constellation Sagittarius, which “produced an image quality within five percent of the primary mission image quality,” NASA stated. More testing is underway.

NASA should have more details at the end of this year as to whether to proceed to a 2014 Senior Review, which is held every two years to review current missions and decide which ones are still worth funding.

Source: NASA

November 26, 2013December 23, 2015 by Elizabeth Howell

Home Computers Discover Gamma-Ray Pulsars

Gamma-ray pulsars in the Milky Way's plane, found by volunteers using Einstein@Home. The sky map is from Fermi's Large Area Telescope. The brighter the color you see, the more intense the radiation in that spot. The small flags show the nationality of the volunteers whose computers spotted the pulsars. Credit: Knispel/Pletsch/AEI/NASA/DOE/Fermi LAT Collaboration

Imagine that you’re innocently running your computer in pursuit of helping data crunch a huge science project. Then, out of the thousands of machines running the project, yours happens to stumble across a discovery. That’s what happened to several volunteers with Einstein@Home, which seeks pulsars in data from the Fermi Gamma-Ray Space Telescope, among other projects.

“At first I was a bit dumbfounded and thought someone was playing a hoax on me. But after I did some research,” everything checked out. That someone as insignificant as myself could make a difference was amazing,” stated Kentucky resident Thomas M. Jackson, who contributed to the project.

Pulsars, a type of neutron star, are the leftovers of stars that exploded as supernovae. They rotate rapidly, with such precision in their rotation periods that they have sometimes been likened to celestial clocks. Although the discovery is exciting to the eight volunteers because they are the first to find these gamma-ray pulsars as part of a volunteer computing project, the pulsars also have some interesting scientific features.

Artist's illustration of a neutron star, a tiny remnant that remains after its predecessor star explodes. Here, the 12-mile (20-kilometer) sphere is compared with the size of Hannover, Germany. Credit: NASA's Goddard Space Flight Center — Artist’s illustration of a neutron star, a tiny remnant that remains after its predecessor star explodes. Here, the 12-mile (20-kilometer) sphere is compared with the size of Hannover, Germany. Credit: NASA’s Goddard Space Flight Center

The four pulsars were discovered in the plane of the Milky Way in an area that radio telescopes had looked at previously, but weren’t able to find themselves. This means that the pulsars are likely only visible in gamma rays, at least from the vantage point of Earth; the objects emit their radiation in a narrow direction with radio, but a wider stripe with gamma rays. (After the discoveries, astronomers used the Max Planck Institute for Radio Astronomy’s 100-meter Effelsberg radio telescope and the Australian Parkes Observatory to peer at those spots in the sky, and still saw no radio signals.)

Two of the pulsars also “hiccup” or exhibit a pulsar glitch, when the rotation sped up and then fell back to the usual rotation period a few weeks later. Astronomers are still learning more about these glitches, but they do know that most of them happen in young pulsars. All four pulsars are likely between 30,000 and 60,000 years old.

Artist's conception of a gamma-ray pulsar. Gamma rays are shown in purple, and radio radiation in green. Credit: NASA/Fermi/Cruz de Wilde — Artist’s conception of a gamma-ray pulsar. Gamma rays are shown in purple, and radio radiation in green. Credit: NASA/Fermi/Cruz de Wilde

“The first-time discovery of gamma-ray pulsars by Einstein@Home is a milestone – not only for us but also for our project volunteers. It shows that everyone with a computer can contribute to cutting-edge science and make astronomical discoveries,” stated co-author Bruce Allen, principal investigator of Einstein@Home. “I’m hoping that our enthusiasm will inspire more people to help us with making further discoveries.”

Einstein@Home is run jointly by the Center for Gravitation and Cosmology at the University of Wisconsin–Milwaukee and the Albert Einstein Institute in Hannover, Germany. It is funded by the National Science Foundation and the Max Planck Society. As for the volunteers, their names were mentioned in the scientific literature and they also received certificates of discovery for their work.

Source: Max Planck Institute for Gravitational Physics

November 26, 2013December 23, 2015 by Elizabeth Howell

NASA Plans To Deepen Asteroid Searches With Planetary Resources

An artist's conception of two tidally locked objects orbiting the Sun from afar. The system: 2010 WG9 may likely look like this. Credit: zmescience

Planetary Resources Inc. — that company that is developing a crowdsourced space telescope to search for asteroids — is planning to work on “crowdsourced software solutions” to make it easier to find asteroids and other near-Earth objects, using NASA-funded data.

NASA announced that Planetary Resources will receive a non-reimbursable Space Act Agreement to help NASA characterize near-Earth objects. It’s the first initiative announced under NASA’s Asteroid Grand Challenge, which the agency announced this summer as a vehicle to find threats to Earth.

A contest is planned in 2014 that will also include participation from the Zooniverse’s forthcoming Asteroid Zoo platform (which includes participation from Planetary Resources). Zooniverse is known for providing ordinary people the chance to participate in astronomical searches, including galaxies and asteroid features.

NASA’s role will be to “develop and manage” the contest, while Planetary Resources is expected to “facilitate the use of NASA-funded sky survey data and help support the algorithm competition and review results,” the agency stated.

NASA is trying mightily to move forward with its plans to capture an explore an asteroid in the next few years, but there’s no guarantee that the agency will receive the funds it wants for it in the fiscal 2014 budget. Politicians have expressed concern that the mission is not interesting the public; besides which, the agency is already battling for funds for its commercial crew and planetary science programs, among others.

Source: NASA

November 25, 2013December 23, 2015 by Elizabeth Howell

Speedy Science: Here’s Four Years Of Herschel Telescope Work In A Short Video

ESA's Herschel telescope used liquid helium to keep cool while it observed heat from the early Universe. Credit: ESA

In just one minute, you can watch the Herschel space telescope painting the sky blue, green and yellow! The colors in this new video represent four years of observations from the European Space Agency telescope, which was active between 2009 and 2013.

“In total, Herschel observed almost a tenth of the entire sky for over 23,500 hours, providing new views into the previously hidden universe, pointing to unseen star birth and galaxy formation, and tracing water through the universe from molecular clouds to newborn stars and to their planet-forming discs and belts of comets,” ESA stated on a video explanation.

As ESA explains, Herschel had two cameras and imaging spectrometers on board, called PACS (Photoconductor Array Camera and Spectrometer, in blue) and SPIRE (Spectral and Photometric Imaging Receiver, in green). When they worked together, their observations are shown in yellow.

Herschel was officially shut down on June 17 — check out the video of those commands here — but the scientific information the telescope produced is still being plumbed by astronomers.

Source: ESA

November 23, 2013December 23, 2015 by Ken Kremer

NASA’s LADEE Probe Starts Science Study of Thin Lunar Atmosphere and Dusty Mystery

Artist’s concept of NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft in orbit above the moon as dust scatters light during the lunar sunset. Credit: NASA Ames / Dana Berry

KENNEDY SPACE CENTER, FL – NASA’s Lunar Atmosphere and Dust Environment Explorer (LADEE) has descended to its planned low altitude orbit and begun capturing science data on its ground breaking mission to study the Moon’s ultra tenuous atmosphere and dust using a spacecraft based on a revolutionary new design aimed at speeding development and cutting costs.

LADEE set sail for Earth’s nearest neighbor during a spectacular night time launch atop the maiden flight of an Air Force Minotaur V rocket on Sept. 6 from NASA’s Wallops Island launch facility on Virginia’s Eastern shore.

The flawless launch thrilled spectators up and down virtually the entire US East coast region and yielded many memorable snapshots.

Following a month long voyage and three and a half long looping orbits of the Earth, LADEE successfully fired its main engine for 4 minutes and 12 seconds on Oct. 6 and successfully entered lunar orbit, Dawn McIntosh, LADEE deputy project manager at NASA Ames Research Center, told Universe Today in an exclusive interview.

A series of engine firings over the past month gradually circularized and lowered LADEE into its final science orbit around our Moon while engineers checked out the spacecraft during the commissioning phase of the mission.

The do or die initial Lunar Orbit Insertion burn (LOI-1) allowed LADEE to be captured into a highly elliptical, equatorial lunar orbit, said McIntosh.

Launch of NASA’s LADEE lunar orbiter on Friday night Sept. 6, at 11:27 p.m. EDT on the maiden flight of the Minotaur V rocket from NASA Wallops, Virginia. Credit: Ken Kremer/kenkremer.com

“Two additional LOI burns on Oct. 6 and Oct 9 lowered LADEE to an approximately 4 hour orbit with a periapsis altitude of 234 Kilometers (km) and apoapsis altitude of 250 km” McIntosh told me.

The trio of LOI main engine firings used up most of LADEE’s precious on board fuel.

“LADEE launched with 134.5 kilograms (kg) of fuel. Post LOI-3, 80% of our fuel has been consumed,” said McIntosh.

“Additional orbit-lowering maneuvers with the orbital control system (OCS) and reaction control system (RCS) of approximately 40 seconds were used to get LADEE into the science orbit.

The spacecraft finally entered its planned two hour science orbit around the moon’s equator on Nov. 20.

Its flying at an extremely low altitude ranging from merely eight to 37 miles (12-60 kilometers) above the moon’s surface.

By circling in this very low altitude equatorial orbit, the washing machine sized probe will make frequent passes crossing from lunar day to lunar night enabling it to precisely measure changes and processes occurring within the moon’s tenuous atmosphere while simultaneously sniffing for uplifted lunar dust in the lunar sky.

The remaining fuel will be used to maintain LADEE’s orbit during the approximately 100 day long science mission. The mission length is dictated by the residual fuel available for thruster firings.

The purpose of LADEE is to collect data that will inform scientists in unprecedented detail about the ultra thin lunar atmosphere, environmental influences on lunar dust and conditions near the surface. In turn this will lead to a better understanding of other planetary bodies in our solar system and beyond.

“A thorough understanding of the characteristics of our lunar neighbor will help researchers understand other small bodies in the solar system, such as asteroids, Mercury, and the moons of outer planets,” said Sarah Noble, LADEE program scientist at NASA Headquarters in Washington.

By studying the raised dust, scientists also hope to solve a 40 year old mystery – Why did the Apollo astronauts and early unmanned landers see a glow of rays and streamers at the moon’s horizon stretching high into the lunar sky.

The $280 million probe is built on a revolutionary ‘modular common spacecraft bus’, or body, that could dramatically cut the cost of exploring space and also be utilized on space probes to explore a wide variety of inviting targets in the solar system.

“LADEE is the first in a new class of interplanetary exploration missions,” NASA Ames Director Worden told Universe Today. “It will study the pristine moon to study significant questions.”

“This is probably our last best chance to study the pristine Moon before there is a lot of human activity there changing things.”

The 844 pound (383 kg) robot explorer was assembled at NASA’s Ames Research Center, Moffett Field, Calif., and is a cooperative project with NASA Goddard Spaceflight Center in Maryland.

LADEE arrived at the Moon last month in the midst of the US government shutdown – which negatively impacted a host of other NASA missions. Only a ‘skeleton crew’ was available.

“All burns went super well,” Worden told me. And he is extremely proud of the entire team of “dedicated” professional men and women who made it possible during the shutdown.

“It says a lot about our people’s dedication and capability when a skeleton crew’ can get a new spacecraft into lunar orbit and fully commissioned in the face of a shutdown!” Worden said to Universe Today.

Now the real science begins for LADEE and the team.

Stay tuned here for continuing LADEE news

Ken Kremer

…………….

Learn more about LADEE, MAVEN, MOM, Mars rovers, Orion and more at Ken’s upcoming presentations

Nov 22-25: “SpaceX launch, MAVEN Mars Launch and Curiosity Explores Mars, Orion and NASA’s Future”, Kennedy Space Center Quality Inn, Titusville, FL, 8 PM

Dec 11: “Curiosity, MAVEN and the Search for Life on Mars”, “LADEE & Antares ISS Launches from Virginia”, Rittenhouse Astronomical Society, Franklin Institute, Phila, PA, 8 PM

November 21, 2013December 23, 2015 by David Dickinson

NASA Halts Work on its New Nuclear Generator for Deep Space Exploration

MSL's MMRTG in the laboratory. (Credit: NASA).

Another blow was dealt to deep space exploration this past weekend. The announcement comes from Jim Green, NASA’s Planetary Science Division Director. The statement outlines some key changes in NASA’s radioisotope program, and will have implications for the future exploration of the outer solar system.

An Advanced Stirling Converter prototype in the laboratory. (Credit: NASA).

We’ve written about the impending plutonium shortage and what it means for the future of spaceflight, as well as the recent restart of plutonium production. NASA is the only space agency that has conducted missions to the outer planets — even the European Space Agency’s Huygens lander had to hitch a ride with Cassini to get to Titan — and plutonium made this exploration possible. Continue reading “NASA Halts Work on its New Nuclear Generator for Deep Space Exploration”

November 21, 2013March 16, 2017 by Fraser Cain

What is a Pulsar?

They are what is known as the “lighthouses” of the universe – rotating neutron stars that emit a focused beam of electromagnetic radiation that is only visible if you’re standing in it’s path. Known as pulsars, these stellar relics get their name because of the way their emissions appear to be “pulsating” out into space.

Not only are these ancient stellar objects very fascinating and awesome to behold, they are very useful to astronomers as well. This is due to the fact that they have regular rotational periods, which produces a very precise internal in its pulses – ranging from milliseconds to seconds.

Description:

Pulsars are types of neutron stars; the dead relics of massive stars. What sets pulsars apart from regular neutron stars is that they’re highly magnetized, and rotating at enormous speeds. Astronomers detect them by the radio pulses they emit at regular intervals.

An artist’s impression of an accreting X-ray millisecond pulsar. The flowing material from the companion star forms a disk around the neutron star which is truncated at the edge of the pulsar magnetosphere. Credit: NASA / Goddard Space Flight Center / Dana Berry

Formation:

The formation of a pulsar is very similar to the creation of a neutron star. When a massive star with 4 to 8 times the mass of our Sun dies, it detonates as a supernova. The outer layers are blasted off into space, and the inner core contracts down with its gravity. The gravitational pressure is so strong that it overcomes the bonds that keep atoms apart.

Electrons and protons are crushed together by gravity to form neutrons. The gravity on the surface of a neutron star is about 2 x 10¹¹ the force of gravity on Earth. So, the most massive stars detonate as supernovae, and can explode or collapse into black holes. If they’re less massive, like our Sun, they blast away their outer layers and then slowly cool down as white dwarfs.

But for stars between 1.4 and 3.2 times the mass of the Sun, they may still become supernovae, but they just don’t have enough mass to make a black hole. These medium mass objects end their lives as neutron stars, and some of these can become pulsars or magnetars. When these stars collapse, they maintain their angular momentum.

But with a much smaller size, their rotational speed increases dramatically, spinning many times a second. This relatively tiny, super dense object, emits a powerful blast of radiation along its magnetic field lines, although this beam of radiation doesn’t necessarily line up with it’s axis of rotation. So, pulsars are simply rotating neutron stars.

And so, from here on Earth, when astronomers detect an intense beam of radio emissions several times a second, as it rotates around like a lighthouse beam – this is a pulsar.

History:

The first pulsar was discovered in 1967 by Jocelyn Bell Burnell and Antony Hewis, and it surprised the scientific community by the regular radio emissions it transmitted. They detected a mysterious radio emission coming from a fixed point in the sky that peaked every 1.33 seconds. These emissions were so regular that some astronomers thought it might be evidence of communications from an intelligent civilization.

Although Burnell and Hewis were certain it had a natural origin, they named it LGM-1, which stands for “little green men”, and subsequent discoveries have helped astronomers discover the true nature of these strange objects.

Astronomers theorized that they were rapidly rotating neutron stars, and this was further supported by the discovery of a pulsar with a very short period (33-millisecond) in the Crab nebula. There have been a total of 1600 found so far, and the fastest discovered emits 716 pulses a second.

Later on, pulsars were found in binary systems, which helped to confirm Einstein’s theory of general relativity. And in 1982, a pulsar was found with a rotation period of just 1.6 microseconds. In fact, the first extrasolar planets ever discovered were found orbiting a pulsar – of course, it wouldn’t be a very habitable place.

Interesting Facts:

When a pulsar first forms, it has the most energy and fastest rotational speed. As it releases electromagnetic power through its beams, it gradually slows down. Within 10 to 100 million years, it slows to the point that its beams shut off and the pulsar becomes quiet.

When they are active, they spin with such uncanny regularity that they’re used as timers by astronomers. In fact, it is said that certain types of pulsars rival atomic clocks in their accuracy in keeping time.

Pulsars also help us search for gravitational waves, probe the interstellar medium, and even find extrasolar planets in orbit. In fact, the first extrasolar planets were discovered around a pulsar in 1992, when astronomers Aleksander Wolszczan and Dale Frail announced the discovery of a multi-planet planetary system around PSR B1257+12 – a millisecond pulsar now known to have two extrasolar planets.

Artist's impression of the planets orbiting PSR B1257+12. Credit: NASA/JPL-Caltech/R. Hurt (SSC) — *Artist’s impression of the planets orbiting PSR B1257+12. Credit: NASA/JPL-Caltech/R. Hurt (SSC)*

It has even been proposed that spacecraft could use them as beacons to help navigate around the Solar System. On NASA’s Voyager spacecraft, there are maps that show the direction of the Sun to 14 pulsars in our region. If aliens wanted to find our home planet, they couldn’t ask for a more accurate map.

We have written many articles about stars here on Universe Today. Here’s an article about a newly discovered gamma ray pulsar, and here’s an article about how millisecond pulsars spin so fast.

If you’d like more information on stars, check out Hubblesite’s News Releases about Stars, and here’s the stars and galaxies homepage.

We have recorded several episodes of Astronomy Cast about stars. Here are two that you might find helpful: Episode 12: Where Do Baby Stars Come From, and Episode 13: Where Do Stars Go When they Die?

November 20, 2013December 23, 2015 by Tammy Plotner

Exploring Our Galaxy’s Ancient Brown Dwarfs

A brown dwarf from the thick-disk or halo is shown. Although astronomers observe these objects as they pass near to the solar system, they spend much of their time away from the busiest part of the Galaxy, and the Milky Way's disk can be seen in the background. Credit: John Pinfield

As the name implies, a brown dwarf is small… only about 7% the size of the Sun. As far as stellar senior citizens go, they’re cool. Zipping along through space at speeds of 100 to 200 kilometers per second, they may have formed back when our galaxy was young – perhaps 10 billion years ago. Now a team of astronomers headed by Dr. David Pinfield at the University of Hertfordshire has identified a pair of the oldest brown dwarfs known… a set of orbs which could be the harbinger of a huge amount of new, unseen objects.

Although we sometimes refer to them as stars, brown dwarfs are in a class of their own. Because they didn’t ignite in nuclear fusion, they don’t generate internal heat like an ordinary star. After they are formed, they continue to cool and fade as time passes. This process makes them very difficult to observe and the discovery of two very old brown dwarfs, with temperatures of 250-600 C is cause for astronomical excitement.

Just how did Pinfield’s team pick such tiny objects out of the vastness of space? The discovery was facilitated thanks to a survey made by the Wide-field Infrared Survey Explorer (WISE), a NASA observatory that scanned the mid-infrared sky from orbit in 2010 and 2011. The ancient objects are cataloged as WISE 0013+0634 and WISE 0833+0052, and they are located in the constellations of Pisces and Hydra. Because they are so elusive, they were also confirmed by large ground-based telescopes (Magellan, Gemini, VISTA and UKIRT).

However, identifying the pair wasn’t easy. Seeing through the eyes of infrared reveals a crowded space – one populated with reddened stars, distant background galaxies and pockets of nebulous gas and dust. Picking out such a small character from a stellar cast would be like finding one tiny pearl in the vastness of an ocean. But Pinfield’s researchers employed a new method which utilizes WISE’s capabilities. As it scanned the sky over and over again, it revealed the cool, brown dwarfs – picking up the faint signature that other searches had missed.

These two particular brown dwarfs are different from the other slow movers of their type. By studying their spectra, the astronomers have identified atmospheres almost entirely comprised of hydrogen. This sets them apart from younger stars which have an abundance of heavier elements. Does being lighter make them speedier? According to Pinfield, “Unlike in other walks of life, the galaxy’s oldest members move much faster than its younger population.”

Stars near to Sun are considered the “local volume” and are created with three overlapping populations – the thin disk, the thick disk and the halo. Each of these layers has a certain amount of age associated with it: the oldest being the thickest and its member stars move up and down at a higher rate of speed. The halo contains both disks, along with the initial materials which formed the very first stars. Thin disk objects abound in the local volume and account for about 97% of the local stars, while thick disk and halo objects are a meager 3%. Chances are, brown dwarfs belong to that smaller percentage which explains why these fast-moving thick-disk/halo objects are only now being revealed.

Just how many may await discovery? Scientists surmise there may be as many as 70 billion brown dwarfs in the galaxy’s thin disk, and the thick disk and halo take up significantly larger galactic volumes. Even at a tiny 3%, this means there could be an army of ancient brown dwarfs in the galaxy. “These two brown dwarfs may be the tip of an iceberg and are an intriguing piece of astronomical archaeology,” said Pinfield. “We have only been able to find these objects by searching for the faintest and coolest things possible with WISE. And by finding more of them we will gain insight into the earliest epoch of the history of the galaxy.”

Original Story Source: Royal Astronomical Society News Release. For further study: “A deep WISE search for very late type objects and the discovery of two halo/thick-disk T dwarfs: WISE 0013+0634 and WISE 0833+0052”, D. J. Pinfield et al, Monthly Notices of the Royal Astronomical Society, in press.