Frost deposits in Louth Crater appears to remain through the year, as found in Mars Reconnaissance Orbiter HiRISE photos of the region. Credit: NASA/JPL/University of Arizona
Mars was once thought to be a fairly unchanging planet, similar to the Moon. But now we know it is a planet that was shaped by water and other forces in the past — and that these forces still come into play today.
Above is a picture of permafrost deposits just discovered in Louth Crater. This find comes from NASA’s Mars Reconnaissance Orbiter’s High Resolution Imaging Science Experiment (HiRISE) and you can see some of its latest water- and dust- shaped environments imaged below.
“A still-unexplained feature of this crater is the diffuse dark smudges visible on the crater floor,” read an update on the University of Arizona HiRISE website explaining this image. “These resemble ‘defrosting spots’ which are visible on carbon dioxide ice in the early spring, but they occur on frost-free areas and survive throughout the summer.”
The frost was caught in a HiRISE image early in the summer, and it persisted as controllers watched it through the summer — indicating that it is permanent. Its size did diminish somewhat, however. Scientists are pretty sure that this is water ice, as carbon dioxide can’t survive the summer.
See more new HiRISE photos below.
A close-up of “chaotic terrain” in Valles Marineris imaged by the Mars Reconnaissance Orbiter’s HiRISE camera. Wind or fluid may have further shaped this region, which could be related to possible signs of an ancient lake found in other regions of Valles Marineris. Credit: NASA/JPL/University of ArizonaA section of the vast Valles Marineris ravine called Melas Chasma, a spot where sulfates (minerals formed in water) have been found before. The image shows layers of deposits that were formed before and after the formation of Valles Marineris. Credit: NASA/JPL/University of ArizonaA section of Eastern Elysium Planitia imaged by the Mars Reconnaissance Orbiter’s HiRISE camera showing a possible old lava field near dust avalanches stirred up more recently. Credit: NASA/JPL/University of Arizona
High resolution image pairs made with HiRISE camera on MRO during Comet Siding Spring's closest approach to Mars on October 19. Shown at top are images of the nucleus region and inner coma. Those at bottom were exposed to show the bigger coma beginning of a tail. Credit: NASA/JPL/Univ. of Arizona
Not to be outdone by the feisty Opportunity Rover, the HiRISE camera on NASA’s Mars Reconnaissance Orbiter (MRO) turned in its homework this evening with a fine image of comet C/2013 Siding Spring taken during closest approach on October 19.
The highest-resolution images were acquired by HiRISE at the minimum distance of 85,750 miles (138,000 km). The image has a scale of 453 feet (138-m) per pixel.
The top set of photos uses the full dynamic range of the camera to accurately depict brightness and detail in the nuclear region and inner coma. Prior to its arrival near Mars astronomers estimated the nucleus or comet’s core diameter at around 0.6 mile (1 km). Based on these images, where the brightest feature is only 2-3 pixels across, its true size is shy of 1/3 mile or 0.5 km. The bottom photos overexpose the comet’s innards but reveal an extended coma and the beginning of a tail extending to the right.
Annotated photo of Comet Siding Spring taken by the Opportunity Rover on October 19 when near closest approach. Credit: NASA/JPL-Caltech/Cornell Univ./ASU/TAMU
To photograph a fast-moving target from orbit, engineers at Lockheed-Martin in Denver precisely pointed and slewed the spacecraft based on comet position calculations by engineers at JPL. To make sure they knew exactly where the comet was, the team photographed the comet 12 days in advance when it was barely bright enough to register above the detector’s noise level. To their surprise, it was not exactly where orbital calculations had predicted it to be. Using the new positions, MRO succeeded in locking onto the comet during the flyby. Without this “double check” its cameras may have missed seeing Siding Spring altogether!
Meanwhile, the Jet Propulsion Lab has released an annotated image showing the stars around the comet in the photo taken by NASA’s Opportunity Rover during closest approach. From Mars’ perspective the comet passed near Alpha Ceti in the constellation Cetus, but here on Earth we see it in southern Ophiuchus not far from Sagittarius.
Comet Siding Spring continues on its way today past the planet Mars in this photo taken on October 20. Copyright: Rolando Ligustri
“It’s excitingly fortunate that this comet came so close to Mars to give us a chance to study it with the instruments we’re using to study Mars,” said Opportunity science team member Mark Lemmon of Texas A&M University, who coordinated the camera pointing. “The views from Mars rovers, in particular, give us a human perspective, because they are about as sensitive to light as our eyes would be.”
After seeing photos from both Earth and Mars I swear I’m that close to picturing this comet in 3D in my mind’s eye. NASA engineers and scientists deserve a huge thanks for their amazing and successful effort to turn rovers and spacecraft, intended for other purposes, into comet observatories in a pinch and then deliver results within 24 hours. Nice work!
Comet C/2013 A1 Siding Spring passed between the Small Magellanic Cloud (left) and the rich globular cluster NGC 130 on August 29, 2014. Credit: Rolando Ligustri
We present here a compendium of Universe Today articles on comet Siding Spring. Altogether 18 Universe Today stories and counting have represented our on-going coverage of a once in a lifetime event. The articles beginning in February 2013, just days after its discovery, lead to the comet’s penultimate event – the flyby of Mars, October 19, 2014. While comet Siding Spring will reach perihelion just 6 days later, October 25, 2014, it will hardly have sensed the true power and impact that our Sun can have on a comet.
Siding Spring’s Oort Cloud cousin, Comet ISON in November 2013 encountered the Sun at a mere 1.86 million km. The intensity of the Sun’s glare was 12,600 times greater than what Siding Spring will experience in a few days. Comet ISON did not survive its passage around the Sun but Comet Siding Spring will soon turn back and begin a very long journey to its place of origin, the Oort Cloud far beyond Pluto.
An animation of comet Siding Springs passage through the inner Solar System. The scale size of its place of origin would dwarf the orbits of the Solar System to little more than a small dot. (Illustration Credit: Near-Earth Object (NEO) office, NASA/JPL)
The closest approach for comet Siding Spring with the Sun – perihelion is at a distance of 1.39875 Astronomical Units (1 AU being the distance between the Earth and Sun), still 209 million km (130 million miles). The exact period of the comet is not exactly known but it is measured in millions of years. In my childhood astronomy book, it stated that comet Halley, when it is at its furthest distance from the Sun, is moving no faster than a galloping horse. This has also been all that comet Siding Spring could muster for millions of years – the slightest of movement in the direction of the Sun.
It is only in the last 3 years, out all the millions spent on its journey, that it has felt the heat of the Sun and been in proximity to the planetary bodies of our Solar System. This is story of all long period comets. A video camera on Siding Spring would have recorded the emergence and evolution of one primate out of several, one that left the trees to stand on two legs, whose brain grew in size and complexity and has achieved all the technological wonders (and horrors) we know of today.
Now with its close encounter with Mars, the planet’s gravity will bend the trajectory of the comet and reduce its orbital period to approximately one million years. No one will be waiting up late for its next return to the inner Solar System.
It is also unknown what force in the depths of the Oort cloud nudged the comet into its encounter with Mars and the Sun. Like the millions of other Oort cloud objects, Siding Spring has spent its existence – 4.5 Billion years, in the darkness of deep space, with its parent star, the Sun, nothing more than a point of light, the brightest star in its sky. The gravitational force that nudged it may have been a passing star, another cometary body or possibly a larger trans-Neptunian object the size of Pluto and even as large as Mars or the Earth.
The forces of nature on Earth cause a constant turning over geological features. Our oceans and atmosphere are constantly recycling water and gases. The comets that we receive from the Oort Cloud are objects as old as our Solar System. Yet it is the close encounter with Mars that has raised the specter of an otherwise small ordinary comet. All these comets from deep space are fascinating gems nearly unaltered for 1/3rd of the time span of the known Universe.
An image of a May 9, 2014 coronal mass ejection from the Sun using data from both the Interface Region Imaging Spectrograph (IRIS) spacecraft and the Solar Dynamics Observatory. Credit: NASA, Lockheed Martin Solar & Astrophysics Laboratory
My, the Sun is a violent place. I mean, we knew that already, but there’s even more evidence for that using new data from a brand-new NASA spacecraft. There’s talk now about tornadoes and jets and even “bombs” swirling amid our Sun’s gassy environment.
A huge set of results from NASA’s Interface Region Imaging Spectrograph (IRIS) spacecraft reveals the true nature of a mysterious transition zone between Sun’s surface and the corona, or atmosphere. Besides the pretty fireworks and videos, these phenomena are telling scientists more about how the Sun moves energy from the center to the outskirts. And, it could tell us more about how stars work in general.
The results are published in five papers yesterday (Oct. 15) in Science magazine. Below, a brief glimpse of what each of these papers revealed about our closest star.
Bombs
This is a heck of a lot of energy packed in here. Raging at temperatures of 200,000 degrees Fahrenheit (111,093 degrees Celsius) are heat “pockets” — also called “bombs” because they release energy quickly. They were found lower in the atmosphere than expected. The paper is here (led by Hardi Peter of the Max Planck Institute for Solar System Research in Gottingen, Germany.)
Tornadoes
It’s a twist! You can see some structures in the chromosphere, just above the Sun’s surface, showing gas spinning like a tornado. They spin around as fast as 12 miles (19 kilometers) a second, which is considered slow-moving on the Sun. The paper is here (led by Bart De Pontieu, the IRIS science lead at Lockheed Martin in California).
High-speed jets
Artist’s impression of the solar wind from the sun (left) interacting with Earth’s magnetosphere (right). Credit: NASA
How does the solar wind — that constant stream of charged particles that sometimes cause aurora on Earth — come to be? IRIS spotted high-speed jets of material moving faster than ever observed, 90 miles (145 kilometers) a second. Since these jets are emerging in spots where the magnetic field is weaker (called coronal holes), scientists suspect this could be a source of the solar wind since the particles are thought to originate from there. The paper is here (led by Hui Tian at the Harvard-Smithsonian Center for Astrophysics in Massachusetts.)
Nanoflares
A solar filament erupts with a coronal mass ejection in this image captured by NASA’s Solar Dynamics Observatory in August 2012. Credit: NASA’s GSFC, SDO AIA Team
Those solar flares the Sun throws off happen when magnetic field lines cross and then snap back into place, flinging particles into space. Nanoflares could do the same thing to heat up the corona, and that’s something else that IRIS is examining. The paper is here (led by Paola Testa, at the Harvard-Smithsonian Center for Astrophysics.)
Structures and more
And here is the transition region in glorious high-definition. Improving on data from the Skylab space station in the 1970s (bottom of video), you can see all sorts of mini-structures on the Sun. The more we learn about these 2,000-mile (3,220-km) objects, the better we’ll understand how heating moves through the Sun. The paper is here (led by Viggo Hansteen, at the University of Oslo in Norway.)
A view of Mimas from the Cassini spacecraft. Credit: NASA/JPL/Space Science Institute
Could there be an ocean hidden somewhere in that Death Star-like picture? This is an image of Mimas, a moon of Saturn, and just yesterday (Oct. 15) newly released data from the Cassini spacecraft suggests there are big liquid reservoirs underneath its surface.
“The amount of the to-and-fro motion indicates that Mimas’ interior is not uniform. These wobbles can be produced if the moon contains a weirdly shaped, rocky core or if a sub-surface ocean exists beneath its icy shell,” said Cornell University in a press release. More flybys with the Cassini spacecraft will be required to learn more about what lies beneath.
You can read more about the study (led by Cornell astronomy research associate Radwan Tajeddine) in Science, where it was published. Below, learn more about other worlds in the Solar System that could host oceans under their surface.
Enceladus
Cassini images of Saturn’s moon Enceladus backlit by the sun show the fountain-like sources of the fine spray of material that towers over the south polar region. This image was taken looking more or less broadside at the “tiger stripe” fractures observed in earlier Enceladus images. It shows discrete plumes of a variety of apparent sizes above the limb (edge) of the moon. This image was acquired on Nov. 27, 2005. Image Credit: NASA/JPL/Space Science Institute
After nearly a decade of speculation, this year the Cassini spacecraft returned gravity data suggesting Enceladus (another moon of Saturn) does have a large subsurface ocean near its south pole, if not a global ocean. If confirmed, that could help explain why scientists see water gushing out of fractures in that area. As this recent paper by Cassini scientists shows, Enceladus is a promising location for habitability.
Titan
A halo of light surrounds Saturn’s moon Titan in this backlit picture, showing its atmosphere. Credit: NASA/JPL/Space Science Institute
By the way, anyone noticed that we still haven’t even left Saturn’s system? Titan is usually high on astrobiology wish lists for researchers because its hydrocarbon chemistry could be precursors to how life evolved. What’s not talked about as much, though, is at least two research findings pointing to evidence of a hidden ocean. Evidence comes from Titan’s tidal flexing from interacting with Saturn — which is 10 times more than what would be expected with a solid core — and the way that it moves on its own axis as well as around Saturn.
Europa
Rendering showing the location and size of water vapor plumes coming from Europa’s south pole. Credit: NASA/ESA/L. Roth/SWRI/University of Cologne
That Minecraft-looking object floating beside Europa there is a rendering showing where water vapor erupted from the Jovian moon, spotted by the Hubble Space Telescope in 2013. We were lucky enough to have a close-up view of Europa in the 1990s and early 2000s courtesy of NASA’s Galileo spacecraft. What we know for sure is there’s thick ice on Europa. What’s underneath is not known, but there’s long been speculation that it could be a subsurface ocean that may have more water than our own planet.
Io
Jupiter’s volcanic moon Io , imaged by the Galileo spacecraft in 1997. Credit: NASA/JPL/University of Arizona
Still flying around Jupiter here, we now turn our attention to Io — a place that is often remarked upon because of its blotchy appearance as well as all of the volcanoes on its surface. A newer analysis of Galileo data in 2011 — looking at some of the lesser-understood magnetic field data signatures — led one research team to conclude there could be a magma ocean lurking underneath that violence.
Triton
A glimpse of Triton from the Voyager 2 spacecraft, which flew by the Neptunian moon in August 1989. Credit: NASA/JPL
Little is known about Triton because only one spacecraft whizzed by it — Voyager 2, which took a running pass through the Neptune system in August 1989. An Icarus paper two years ago speculated that the world could host a subsurface ocean, but more data is needed. The energy of Neptune (which captured Triton long ago) could have melted its interior through tidal heating, possibly creating water from the ice in its crust.
Charon
Hubble image of Pluto and some of its moons, Charon, Nix and Hydra. Image Credit: NASA, ESA, H. Weaver (JHU/APL), A. Stern (SwRI), and the HST Pluto Companion Search Team
We don’t have any close-up pictures of this moon of Pluto yet, but just wait a year. The New Horizons spacecraft will zoom past Charon and the rest of the system in July 2015. In the meantime, however, findings based on a model came out this summer in Icarus suggesting Charon — despite being so far from the Sun — might have had a subsurface ocean in the past. Or even now. The key is its once eccentric orbit, which would have produced tidal heating while interacting with Pluto. The science team plans to look for cracks that could be indicative of “the structure of the moon’s interior and how easily it deforms, and how its orbit evolved,” stated Alyssa Rhoden of NASA’s Goddard Space Flight Center in Maryland, who led the research.
NOAA's GOES-East satellite captured this image of Hurricane Gonzalo off the U.S. East Coast on Oct. 16 at 13:07 UTC (9:07 a.m. EDT). Gonzalo is classified as Category 4 storm. Credit: NASA/NOAA GOES Project
Hurricane Gonzalo, the first major Atlantic Ocean basin hurricane in three years, has strengthened to a dangerous Category 4 storm, threatening Bermuda and forcing a postponement of the upcoming launch of the Orbital Sciences Antares rocket to the space station from the Virginia shore to no earlier than Oct. 27.
A hurricane warning is in effect for the entire island of Bermuda.
NASA and Orbital Sciences had no choice but to delay the Antares blastoff from Oct. 24 to no earlier than Oct. 27 because Bermuda is home to an “essential tracking site” that must be operational to ensure public safety in case of a launch emergency situation.
Antares had been slated for an early evening liftoff with the Cygnus cargo carrier on the Orb-3 mission to the International Space Station (ISS).
NASA and Orbital issued the following statement:
“Due to the impending arrival of Hurricane Gonzalo on the island of Bermuda, where an essential tracking site used to ensure public safety during Antares launches is located, the previously announced “no earlier than” (NET) launch date of October 24 for the Orb-3 CRS mission to the International Space Station for NASA is no longer feasible.”
Orbital Sciences Corporation Antares rocket and Cygnus spacecraft prior to blast off on July 13 2014 from Launch Pad 0A at NASA Wallops Flight Facility , VA, on the Orb-2 mission bound for the International Space Station. Credit: Ken Kremer – kenkremer.com
The powerful Gonzalo is currently expected to make a direct hit on Bermuda on Friday afternoon, Oct. 17. It’s packing devastating maximum sustained winds exceeding 145 mph (225 kph).
NASA and NOAA satellites including the Terra, Aqua and GOES-East satellites are providing continuous coverage of Hurricane Gonzalo as it moves toward Bermuda, according to a NASA update today.
The ISS-RapidScat payload tracking ocean winds, that was just attached to the exterior of the ISS, is also designed to help with hurricane monitoring and forecasting.
Tropical storm force winds and 20 to 30 foot wave heights are expected to impact Bermuda throughout Friday and continue through Saturday and into Sunday.
“The National Hurricane Center expects hurricane-force winds, and rainfall totals of 3 to 6 inches in Bermuda. A storm surge with coastal flooding can be expected in Bermuda, with large and destructive waves along the coast. In addition, life-threatening surf and riptide conditions are likely in the Virgin Islands, Puerto Rico, Dominican Republic, Bahamas. Those dangerous conditions are expected along the U.S. East Coast and Bermuda today, Oct. 16,” according to NASA.
On Oct. 15 at 15:30 UTC (11:30 a.m. EDT) NASA’s Terra satellite captured this image of Hurricane Gonzalo in the Atlantic Ocean. Credit: NASA Goddard MODIS Rapid Response Team
After the hurricane passes, a team will be sent to assess the impact of the storm on Bermuda and the tracking station. Further delays are possible if Bermuda’s essential infrastructure systems are damaged, such as power, transportation and communications.
The Antares/Cygnus rocket and cargo ship launch from the Mid-Atlantic Regional Spaceport at NASA’s Wallops Flight Facility along the eastrn shore of Virginia.
Liftoff is currently target for October 27 at 6:44 p.m. (EDT). The rendezvous and berthing of Cygnus with the ISS remains on November 2, with grapple of the spacecraft by the station’s robotic arm at approximately 4:58 a.m. (EST), according to a NASA update.
Stay tuned here for Ken’s continuing Earth and Planetary science and human spaceflight news.
NASA astronaut Reid Wiseman (Expedition 41) captured during an Oct. 15 spacewalk by fellow astronaut Butch Wilmore. Credit: Reid Wiseman / Twitter
What a view! NASA’s Reid Wiseman and Butch Wilmore spacewalked successfully yesterday (Oct. 15) for more than 6.5 hours, replacing a faulty camera as well as a broken power regulator that was reducing the amount of power available on the International Space Station. The astronauts also shifted equipment to get ready for some bigger upgrades on station to prepare for commercial spacecraft arriving in 2017.
Check out the stunning pictures from the spacewalk below.
Two potential targets for the New Horizons mission emerge in these Hubble Space Telescope multiple-exposure images. Both are about four billion miles (6.4 billion kilometers) away. NASA, ESA, SwRI, JHU/APL, and the New Horizons KBO Search Team
Where could New Horizons visit after it flies by Pluto next year? NASA’s Hubble Space Telescope is on the case. In a program that pushed the limits of the 24-year-old observatory, Hubble found three potential Kuiper Belt Objects for the spacecraft to visit.
The wrinkle is there is no money approved yet for New Horizons to do an extended mission yet, but team members (including Alex Parker from the Southwest Research Institute, who is quoted from Twitter below) are celebrating the milestone. To them, the most promising target (PT1) is the one on the left of the images you see above. Read more about it below the jump.
The Kuiper Belt is a zone of icy objects about four billion miles (6.4 billion kilometers) from the Sun, considered to be leftovers of the building blocks that put together the Solar System billions of years ago. It’s an area that Pluto itself drifts through from time to time on its elliptical orbit around the Sun. Roughly 1,000 objects there have been cataloged, although many more are believed to exist.
The team used Hubble from June 16 to 26 in a test program to look at 20 sky zones for evidence of KBOs, finding two that had never been spotted before by ground-based telescopes. More searching between July and September revealed one object that is “definitely reachable”, NASA stated, and two others that require more scrutiny.
We estimate that PT1 is several 10s of kilometers across. Here’s what that looks like next to Cape Cod and #Comet67P: pic.twitter.com/IHUx6uymO7
Here is where PT1 lies in relation to the rest of the solar system. The yellow path is New Horizons’ trajectory. pic.twitter.com/4aQDEj8oPZ — Alex Parker (@Alex_Parker) October 15, 2014
Here is a gif of the Hubble Space Telescope discovery images of our New Horizons-targetable Kuiper Belt Object PT1. http://t.co/ifw8I4a8Wz
An important and sobering note: even though New Horizons can reach this Kuiper Belt Object, there is no guarantee of an extended mission. — Alex Parker (@Alex_Parker) October 15, 2014
Each of the three candidates would take a while to reach, as they are all about one billion miles (1.6 billion km) beyond Pluto. They’re also tiny, with two estimated at 34 miles (55 kilometers) across and the third at 15 miles (25 kilometers). This makes them 10 times bigger than the average comet, but only 1-2% the size of small Pluto.
“This was a needle-in-haystack search for the New Horizons team because the elusive KBOs are extremely small, faint, and difficult to pick out against a myriad background of stars in the constellation Sagittarius, which is in the present direction of Pluto,” NASA wrote in a press release.
New Horizons’ team plans to ask for the extended mission in late 2016. Meanwhile, the spacecraft (which has been flying ever outwards since 2006) will finally zoom past its main target of Pluto in July 2015.
A view of the crater Prokofiev on Mercury. The crater is the largest one on the planet's north pole area to have "radar-bright" material, a probable sign of ice. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.
New pictures of water ice at Mercury’s north pole — the first such optical images ever — could help scientists better understand how water came to planets in the rest of the Solar System, including Earth. The image you see above came courtesy of NASA’s MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft.
Mercury is a hot planet (it’s the closest one to the Sun), so the only way the ice survives is in deep shadow. This makes it hard to spot unless scientists use some clever techniques. In this case, they examined some scattered light from Prokofiev, the biggest crater in Mercury’s north pole suspected to hold the deposits.
The pictures show that Prokofiev’s surface water ice likely arrived after the craters underneath. And in an intriguing find, there is probably other water ice sitting under dark materials believed to be “frozen organic-rich compounds,” stated the Johns Hopkins University Applied Physics Laboratory.
“This result was a little surprising, because sharp boundaries indicate that the volatile deposits at Mercury’s poles are geologically young, relative to the time scale for lateral mixing by impacts,” stated lead researcher Nancy Chabot, the Instrument Scientist for MESSENGER’s Mercury dual imaging system.
Illustration of MESSENGER in orbit around Mercury (NASA/JPL/APL)
“One of the big questions we’ve been grappling with is ‘When did Mercury’s water ice deposits show up?’ Are they billions of years old, or were they emplaced only recently?”, added Chabot, who is a planetary scientist at the Johns Hopkins University Applied Physics Laboratory in Maryland. “Understanding the age of these deposits has implications for understanding the delivery of water to all the terrestrial planets, including Earth.”
Another intriguing property comes when scientists compare Mercury to the Moon: because the ice looks different on both relatively atmosphere-less bodies, scientists believe the water came more recently to the Moon. But more study is required.
An artists illustration of the early Universe. Image Credit: NASA
There’s nothing more out of this world than quasi-stellar objects or more simply – quasars. These are the most powerful and among the most distant objects in the Universe. At their center is a black hole with the mass of a million or more Suns. And these powerhouses are fairly compact – about the size of our Solar System. Understanding how they came to be and how — or if — they evolve into the galaxies that surround us today are some of the big questions driving astronomers.
Now, a new paper by Yue Shen and Luis C. Ho – “The diversity of quasars unified by accretion and orientation” in the journal Nature confirms the importance of a mathematical derivation by the famous astrophysicist Sir Arthur Eddington during the first half of the 20th Century, in understanding not just stars but the properties of quasars, too. Ironically, Eddington did not believe black holes existed, but now his derivation, the Eddington Luminosity, can be used more reliably to determine important properties of quasars across vast stretches of space and time.
A quasar is recognized as an accreting (meaning- matter falling upon) super massive black hole at the center of an “active galaxy”. Most known quasars exist at distances that place them very early in the Universe; the most distant is at 13.9 billion light years, a mere 770 million years after the Big Bang. Somehow, quasars and the nascent galaxies surrounding them evolved into the galaxies present in the Universe today. At their extreme distances, they are point-like, indistinguishable from a star except that the spectra of their light differ greatly from a star’s. Some would be as bright as our Sun if they were placed 33 light years away meaning that they are over a trillion times more luminous than our star.
An artists illustration of the central engine of a quasar. These “Quasi-stellar Objects” QSOs are now recognized as the super massive black holes at the center of emerging galaxies in the early Universe. (Photo Credit: NASA)
The Eddington luminosity defines the maximum luminosity that a star can exhibit that is in equilibrium; specifically, hydrostatic equilibrium. Extremely massive stars and black holes can exceed this limit but stars, to remain stable for long periods, are in hydrostatic equilibrium between their inward forces – gravity – and the outward electromagnetic forces. Such is the case of our star, the Sun, otherwise it would collapse or expand which in either case, would not have provided the stable source of light that has nourished life on Earth for billions of years.
Generally, scientific models often start simple, such as Bohr’s model of the hydrogen atom, and later observations can reveal intricacies that require more complex theory to explain, such as Quantum Mechanics for the atom. The Eddington luminosity and ratio could be compared to knowing the thermal efficiency and compression ratio of an internal combustion engine; by knowing such values, other properties follow.
Several other factors regarding the Eddington Luminosity are now known which are necessary to define the “modified Eddington luminosity” used today.
The new paper in Nature shows how the Eddington Luminosity helps understand the driving force behind the main sequence of quasars, and Shen and Ho call their work the missing definitive proof that quantifies the correlation of a quasar properties to a quasar’s Eddington ratio.
They used archival observational data to uncover the relationship between the strength of the optical Iron [Fe] and Oxygen[O III] emissions – strongly tied to the physical properties of the quasar’s central engine – a super-massive black hole, and the Eddington ratio. Their work provides the confidence and the correlations needed to move forward in our understanding of quasars and their relationship to the evolution of galaxies in the early Universe and up to our present epoch.
Astronomers have been studying quasars for a little over 50 years. Beginning in 1960, quasar discoveries began to accumulate but only through radio telescope observations. Then, a very accurate radio telescope measurement of Quasar 3C 273 was completed using a Lunar occultation. With this in hand, Dr. Maarten Schmidt of California Institute of Technology was able to identify the object in visible light using the 200 inch Palomar Telescope. Reviewing the strange spectral lines in its light, Schmidt reached the right conclusion that quasar spectra exhibit an extreme redshift and it was due to cosmological effects. The cosmological redshift of quasars meant that they are at a great distance from us in space and time. It also spelled the demise of the Steady-State theory of the Universe and gave further support to an expanding Universe that emanated from a singularity – the Big Bang.
Dr. Maarten Schmidt, Caltech, with Donald Lynden-Bell, were the first recipients of the Kavli Prize in Astrophysics, “for their seminal contributions to understanding the nature of quasars”. While in high school, this author had the privilege to meet Dr. Schmidt at the Los Angeles Museum of Natural History after his presentation to a group of students. (Photo Credit: Caltech)
The researchers, Yue Shen and Luis C. Ho are from the Institute for Astronomy and Astrophysics at Peking University working with the Carnegie Observatories, Pasadena, California.
