15,000 Galaxies in One Image

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Astronomers have just assembled one of the most comprehensive portraits yet of the universe’s evolutionary history, based on a broad spectrum of observations by the Hubble Space Telescope and other space and ground-based telescopes.  Each of the approximately 15,000 specks and spirals are galaxies, widely distributed in time and space. (NASA, ESA, P. Oesch of the University of Geneva, and M. Montes of the University of New South Wales)

Here’s an image to fire your imagination: Fifteen thousand galaxies in one picture — sources of light detectable today that were generated as much as 11 billion years ago.

Of those 15,000 galaxies, some 12,000 are inferred to be in the process of forming stars.  That’s hardly surprising because the period around 11 billions years ago has been determined to be the prime star-forming period in the history of the universe.  That means for the oldest galaxies in the image, we’re seeing light that left its galaxy but three billion years after the Big Bang.

This photo mosaic, put together from images taken by the Hubble Space Telescope and other space and ground-based telescopes, does not capture the earliest galaxies detected. That designation belongs to a galaxy found in 2016 that was 420 million years old at the time it sent out the photons just collected. (Photo below.)

Nor is it quite as visually dramatic as the iconic Ultra Deep Field image produced by NASA in 2014. (Photo below as well.)

But this image is one of the most comprehensive yet of the history of the evolution of the universe, presenting galaxy light coming to us over a timeline up to those 11 billion years.  The image was released last week by NASA and supports an earlier paper in The Astrophysical Journal by Pascal Oesch of Geneva University and a large team of others.

And it shows, yet again, the incomprehensible vastness of the forest in which we are a tiny leaf.

Some people apparently find our physical insignificance in the universe to be unsettling.  I find it mind-opening and thrilling — that we now have the capability to not only speculate about our place in this enormity, but to begin to understand it as well.

The Ultra-Deep field composite, which contains approximately 10,000 galaxies.  The images were collected over a nine-year period.  {NASA, ESA, H. Teplitz and M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (Arizona State University), and Z. Levay (STScI)} 

For those unsettled by the first image, here is the 2014 Ultra Deep Field image, which is 1/14 times the area of the newest image.  More of the shapes in this photo look to our eyes like they could be galaxies, but those in the first image are essentially the same.

In both images, astronomers used the ultraviolet capabilities of the Hubble, which is now in its 28th year of operation.

Because Earth’s atmosphere filters out much ultraviolet light, the space-based Hubble has a huge advantage because it can avoid that diminishing of ultraviolet light and provide the most sensitive ultraviolet observations possible.

That capability, combined with infrared and visible-light data from Hubble and other space and ground-based telescopes, allows astronomers to assemble these ultra deep space images and to gain a better understanding of how nearby galaxies grew from small clumps of hot, young stars long ago.

The light from distant star-forming regions in remote galaxies started out as ultraviolet. However, the expansion of the universe has shifted the light into infrared wavelengths.

These images, then,  straddle the gap between the very distant galaxies, which can only be viewed in infrared light, and closer galaxies which can be seen across a broad spectrum of wavelengths.

The farthest away galaxy discovered so far is called GN-z11 and is seen now as it was 13.4 billion years in the past.  That’s  just 400 million years after the Big Bang.

GN-z11 is surprisingly bright infant galaxy located in the direction of the constellation of Ursa Major. Thus NASA video explains much more:

The farthest away galaxy ever detected — GN-z11. {NASA, ESA, P. Oesch (Yale University, Geneva University), G. Brammer (STScI), P. van Dokkum (Yale University), and G. Illingworth (University of California, Santa Cruz)} 

 

Galaxy formation chronology, showing GN-z11 in context. Hubble spectroscopically confirmed the farthest away galaxy to date. {NASA, ESA, P. Oesch and B. Robertson (University of California, Santa Cruz), and A. Feild (STScI)}

In addition representing cutting-edge science — and enabling much more — these looks into the most distant cosmic past offer a taste of what the James Webb Space Telescope, now scheduled to launch in 2021, is designed to explore.  It will have greatly enhanced capabilities to explore in the infrared, which will advance ultra-deep space observing.

But putting aside the cosmic mysteries that ultra deep space and time astronomy can potentially solve, the images available today from Hubble and other telescopes are already more than enough to fire the imagination about what is out there and what might have been out there some millions or billions of years ago.

A consensus of exoplanet scientists holds that each star in the Milky Way galaxy is likely to have at least one planet circling it, and our galaxy alone has billions and billions of stars.  That makes for a lot of planets that just might orbit at the right distance from its host star to support life and potentially have atmospheric, surface and subsurface conditions that would be supportive as well.

A look these deep space images raises the question of how many of them also house stars with orbiting planets, and the answer is probably many of them.  All the exoplanets identified so far are in the Milky Way, except for one set of four so far.

Their discovery was reported earlier this year by Xinyu Dai, an astronomer at the University of Oklahoma, and his co-author, Eduardo Guerras.  They came across what they report are planets while using NASA’s Chandra X-ray Observatory to study the environment around a supermassive black hole in the center of a galaxy located 3.8 billion light-years away from Earth.

In The Astrophysical Journal Letters , the authors report the galaxy is home to a quasar, an extremely bright source of light thought to be created when a very large black hole accelerates material around it. But the researchers said the results of their study indicated the presence of planets in a galaxy that lies between Earth and the quasar.

Furthermore, the scientists said results suggest that in most galaxies there are hundreds of free-floating planets for every star, in addition to those which might orbit a star.

The takeaway for me, as someone who has long reported on astrobiology and exoplanets, is that it is highly improbable that there are no other planets out there where life occurs, or once occurred.

As these images make clear, the number of planets that exist or have existed in the universe is essentially infinite.  That no others harbor life seems near impossible.

 

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Back to the Future on the Moon

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There have been no humans on the surface of the moon since the Apollo program ended in 1972.  Now, in addition to NASA, space agencies in India, China, Russia, Japan and Europe and developing plans to land humans on the moon. (NASA/Robin Lee)

What does NASA’s drive to return to the moon have to do with worlds of exoplanets and astrobiology that are generally discussed here?  The answer is actually quite a lot.

Not so much about the science, although current NASA plans would certainly make possible some very interesting science regarding humans living in deep space, as well as some ways to study the moon, Earth and our sun.

But it seems especially important now to look at what NASA and others have in mind regarding our moon because the current administration has made a top priority of returning landers and humans to there, prospecting for resources on the moon and ultimately setting up a human colony on the moon.

This has been laid out in executive directives and now is being translated into funding for NASA (and commercial) missions and projects.

There are at least two significant NASA projects specific to the moon initiative now planned, developed and in some cases funded.  They are the placement of a small space station that would orbit the moon, and simultaneously a series of robotic moon landings — to be conducted by commercial ventures but carrying NASA and other instruments from international and other commercial partners.

The goal is to start small and gradually increase the size of the landers until they are large enough to carry astronauts.

And the same growth line holds for the overall moon mission.  The often-stated goal is to establish a colony on the moon that will be a signal expansion of the reach of humanity and possibly a significant step towards sending humans further into space.

A major shift in NASA focus is under way and, most likely in the years ahead, a shift in NASA funding.

Given the potential size and importance of the moon initiative — and its potential consequences for NASA space science — it seems valuable to both learn more about it.

 

Cislunar space is, generally speaking, the area region between the Earth and the moon. Always changing because of the movements of the two objects.

Development work is now under way for what is considered to be the key near-term and moon-specific project.  It used to be called the the Deep Space Gateway as part of the Obama administration proposal for an asteroid retrieval mission, but now it’s the Lunar Orbital Platform-Gateway (LOP-G.)

If built, the four-person space station would serve as a quasi-permanent outpost orbiting the moon that advocates say would enhance exploration and later commercial exploitation of the moon.  It would provide a training area and safe haven for astronauts, could become a center for moon, Earth and solar science, and could continue and expand the international cooperation nurtured on the International Space Station (ISS) project for several decades.

In its Gateway Memorandum, published last month, NASA and the administration also made clear that the station would have, as a central goal, geopolitical importance.

As stated in the memorandum, “the next step in human spaceflight is the establishment of U.S. preeminence in cislunar space through the operations and the deployment of a U.S.-led lunar orbital platform,  “Gateway.”  (“Cislunar space” is the region lying  between the Earth and the moon.)

The administration requested $500 million for planning the LOP-G project in fiscal 2019.  The first component to be built and hopefully launched into cislunar space under the plan is the “power and propulsion element.”

 

An artist version of a completed Gateway spaceport with the Orion capsule approaching. (NASA)

Five companies have put together proposals for the “PPE,” and NASA officials have said they are ready to move ahead with procurement.

During a March meeting of the NASA Advisory Council’s human exploration and operations committee, Michele Gates, director of the Power and Propulsion Element at NASA Headquarters, said the agency will be ready to move ahead with procurement of the module when the five industry proposals are completed.

Some of those companies had been involved in studies for the cancelled Asteroid Redirect Mission and Gates said, “Our strategy is to leverage all of the work that’s been done, including on the Asteroid Redirect Mission.”

Five different companies have contracts to design possible space station habitation modules as well.

So the plan has some momentum.  If all moves ahead as described, NASA will launch the components of the Gateway in the early to mid 2020s.  More than a dozen international agencies have voiced interest in joining the project, including European, Japanese, Canadian and other ISS partners.

As part of that outreach, an informal partnership agreement has already been signed with Roscosmos, the Russian space agency, with the possibility of using a future Russian heavy rocket to help build the station and ferry crew.

 

Astronaut John Young of the Apollo 16 mission on the moon. The primary goal of the NASA moon initiative is to return astronauts to the surface.(NASA)

The other NASA moon initiative involves an effort to send many robotic landers to the moon to look for potential water and fuel (hydrogen) to be collected for a cislunar and ultimately lunar economy.

NASA had worked for some time on what was called a Resource Prospector, a mission to study water ice and other volatiles at the lunar poles.  But this spring NASA Administrator Jim Bridenstine announced the Prospector was being cancelled because it was not suited to the what is called the new Exploration Campaign — NASA’s concept for a series of missions that will initially use small, commercially developed landers, followed by larger landers.

So the Prospector project is now considered “too limited in scope for the agency’s expanded lunar exploration focus,” the agency said in a statement. “NASA’s return to the moon will include many missions to locate, extract and process elements across bigger areas of the lunar surface.”

The agency also says it will rely on private companies to design and build the landers, as well as launching them into space.

So these are the out-of-the gate projects NASA has in mind for the moon. They, however, are hardly where the big money is going.  That is directed to the heavy rocket under development and construction for more than a decade (the Space Launch System, or SLS) and the Orion space capsule.

They are designed to be the main conduits to the Gateway and perhaps beyond some day, and they have been enormously costly to build — at least $22 billion to construct up through 2021, NASA officials told the Government Accounting Office in 2014. And that doesn’t include the more costly second SLS rocket scheduled for 2023 with a crew aboard.

What’s more, it is estimated to cost at least $1.5 billion to launch each SLS/Orion voyage in years ahead.

 

Astronauts go into an Orion capsule mock-up. The un-manned spacecraft is expected to be ready for launch in 2020. (NASA/ Bill Stafford and Roger Markowitz)

 

Another mock-up of the inside of the Orion crew module, which carries four astronauts and is scheduled to launch in 2023. It has 316 cubic feet of habitable space, compared with 210 cubic feet for the Apollo capsules. (NASA)

 

Since this column is primarily about space and origins science, I was drawn to the conference held late Feb. in Denver — billed as the Deep Space Gateway Concept Science Workshop.  The idea, surely, was to share and showcase what science might be achievable on the mini-space station.

As you might imagine, a major scientific focus was on the challenges to humans of living in deep space and techniques that might be used to mitigate problems. Abstracts included studies of the effects of radiation on astronauts, on drugs, on food, on the immune system and more.

NASA and others have studied for years radiation and micro-gravity effects on astronauts aboard the International Space Station, but conditions in a deep space environment would be quite a bit different.  Probably most importantly, astronauts aboard the Gateway would be exposed to much more dangerous radiation than those in the ISS because that low-Earth orbit station is protected by the Van Allen radiation belts.

There was also an intriguing proposal to study the ability of lunar regolith (the rock, dust and gravel on the surface) to shield growing plants on the station from radiation, and others on the role and usefulness of plants and micro-organisms in deep space.

Scientists also proposed many different ways to study the moon, the Earth and the sun.  Harley Thronson of NASA Goddard, one of the moderators of the conference, said that sun scientists seemed especially excited by the opportunities the Gateway could offer.

As far as I could tell, there was but one proposal that involved astrobiology or exoplanets.  It was a plan by scientists from SETI and NASA Ames to study Earth with a spectrometer as a way to understand and measure potential bio-markers on exoplanets.

So there’s undoubtedly good science to be done on a lunar space port regarding human space flight, the moon, the Earth and sun.

What I wonder is this:  Will this new, intense and costly lunar focus on the moon take away from what I like to think of as The Golden Age of Space Science — the unending breakthroughs of recent decades in understanding planets and distant moons in our solar system, detecting and characterizing the billions and billions of exoplanets out there,  as well as revealing the structure and history of the cosmos.

 

The Sombrero Galaxy, as imaged by the Hubble Space Telescope, NASA’s Flagship observatory of the 1990s. The James Webb Space Telescope is delayed but is expected to provide the same remarkable images and science as Hubble once it’s up and working.  WFIRST, the planned flagship observatory of the 2020s was cancelled by the administration earlier this year because of a NASA funding shortfall, but its fate remains undecided. (NASA)

I’m not thinking about today but about when costly NASA flagship space observatories or major planetary missions come up for approval, or non-approval, in the future.  Will the funding, and the deep interest, still be there?

Others more knowledgeable about the mechanics of space travel also criticize the Gateway as a costly detour from what long has been considered the main goal of space exploration — sending humans to Mars — and as redundant when it comes to accessing and studying the moon.

On a more encouraged note, a lunar station and lunar base could become part of a much larger space architecture that will allow for all kinds of advances in the decades ahead.  This is precisely the kind of build-out that Thronson, who is Senior Scientist for Advanced Astrophysics Mission Concepts at NASA Goddard and Chief Technologist for the Cosmic Origins and Physics of the Cosmos Program Offices, has been working towards for years.

Ever mindful of the uses of such a space architecture, he pointed out one potential use of a lunar space station that is seldom heard:  If a powerful new telescope in deep space needs repair or upgrading, he wrote in an email, there’s no way to get humans to it now.  The Hubble Space Telescope could be fixed because it was not in deep space and astronauts could get to it.

Thronson sees a potential parallel use for the Gateway, as he described in an email. “My astronomy colleagues, including myself, have been for many years advocating using a Gateway-type facility to assemble, repair, and upgrade the next generation (and beyond) of major astronomical missions. Nothing beats having a human on site, if there are complicated activities that need to be carried out.”

 

 

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The Mars Water Story Gets Ever More Interesting

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Enchanced-color traverse section of Martian icy scarps in late spring to early summer. Arrows indicate locations where relatively blue material is particularly close to the surface. Image taken by HiRISE camera on Mars Reconnaissance Orbiter. (NASA/JPL/UNIVERSITY OF ARIZONA/USGS )

Huge escarpments of quite pure water ice have been found in the Southern Highlands of Mars — accessible enough that astronauts might some day be able to turn the ice into water, hydrogen and oxygen.

Some of these deposits are more than 100 meters thick and begin only a meter or two below the surface.

These are among the conclusion from a new paper in the journal Science that describes these previously unknown water ice reserves.  While Mars scientists have long theorized the presence of subsurface ice under one-third of the planet, and even exposed bits of it with the Phoenix lander, the consensus view was that Martian ice was generally cemented with soil to form a kind of permafrost.

But the “scarp” ice described by Colin Dundas of the U.S. Geological Survey and colleagues is largely water ice without much other material.  This relative purity, along with its accessibility, would make the ice potentially far more useful to future astronauts.

“The ice exposed by the scarps likely originated as snow that transformed into massive ice sheets, now preserved beneath less than 1 to 2 meters of dry and ice-cemented dust or regolith,” the authors write. The shallow depths, the write “make the ice sheets potentially accessible to future exploration.”

The bright red regions contain water ice, as determined by measurements by the High-Resolution Imaging Science Experiment (HiRISE) on NASA’s Mars Reconnaissance Oribter. (NASA)

The importance is clear:  These sites are “very exciting” for potential human bases as well, says Angel Abbud-Madrid, director of the Center for Space Resources at the Colorado School of Mines in Golden, who led a recent NASA study exploring potential landing sites for astronauts.

Water is a crucial resource for astronauts, because it could be combined with carbon dioxide, the main ingredient in Mars’s atmosphere, to create oxygen to breathe and methane, a rocket propellant. And although researchers suspected the subsurface glaciers existed, they would only be a useful resource if they were no more than a few meters below the surface. The ice cliffs promise abundant, accessible ice, Abbud-Madrid told Science Magazine.

While the discovery adds to the view that Mars is neither bone-dry now nor was earlier in its history, it does not necessarily add to the question of where all the Martian water has gone or how much was originally there.

That’s because the paper describes the huge ice deposits as the result of snowfall over more recent eons that was packed into its current form, rather than water that might have been present during the warmer wetter periods of Mars history. With this in mind, Dundas said in an email that his team’s work does not add to what is known about the early Mars water budget.

As for the age of the water ice, he said “we can’t put an accurate number on it at this time, but the icy units are lightly cratered. Others in the community have proposed snowfall during periods of high axial tilt within the last few million years.”

So the ice is relatively young. But that doesn’t mean it has no story to tell.  Exposed ice, like exposed rock, always has a story to tell.

“We expect the vertical structure of Martian ice-rich deposits to preserve a record of ice deposition and past climate,” the authors write.

The eight scarps studied were steep and faced the poles. All were in the mid-latitudes, and therefore far from the polar ice sheets.

The lander Phoenix dug into the soil of the northern polar region and found cemented ice as well as pure ice several inches down. (NASA)

NASA has long had a motto for exploring Mars and other sites beyond Earth of “follow the water.”  That has been expanded to “follow the carbon” and “follow the organics,” but the water is still a guidepost of sorts of where life, or its remnants, might be found.  Now with these large and seemingly accessible deposits of water ice, “follow the water” takes on a new meaning for potential future astronauts in search of essential chemical components.

Still, the issue of just how much water there is and has been on Mars is a central to piecing together the planet’s history and how much of the planet might have one day been eminently habitable.

The last decade of Mars exploration and observation has led most Mars scientists to conclude that the planet once had rivers, lakes and possibly a northern ocean. That water is almost entirely (or perhaps entirely) gone from the surface now, and understanding where it went is certainly key to understanding the history of the planet.

While much no doubt escaped to space after the early protective Mars magnetic field and atmosphere largely disappeared, researchers say there remains a lot of Mars water to be accounted for.

An article in the journal Nature last month reported the possibility of large amounts of water mixing with Martian basalts long ago and forming a broadly water-rich crust.  The authors of that paper, led by Jon Wade of Oxford’s Department of Earth Sciences, described modeling that found water on early Mars could be absorbed into spongy rock at a far greater rate than on Earth.

In an accompanying review, geochemist and cosmochemist Tomohiro Usui of the Earth-Life Science Institute in Tokyo, supported the notion, and added another possibility that he has published on as well.

“Ground ice might also account for the missing water reservoir on Mars,” he wrote. “Subsurface radar-sounder measurements have detected an anomaly in an electrical property of rocks in the planet’s northern hemisphere, which implies that massive ice deposits are embedded among or between layers of sediment and volcanic materials at a depth of 60–80 m.”

Usui wrote that the ground-ice model has also been proposed based of analyses of hydrogen isotopes in Martian meteorites and of the shapes and characteristics of craters. Indeed, the crater study indicated that the subsurface water ice has a volume comparable to the size of the ancient oceans.

Where did the large amounts of water once present on Mars go. Some clearly was lost to the atmosphere, but some researchers are convinced that much is underground as ice or incorporated into minerals. (Nature)

 

Dundas agreed that the new paper was a continuation of earlier work, rather than something entirely new. “We’ve known for some time that there is shallow ground ice within a meter of the surface, and there have been recent radar detections of ice sheets tens of meters thick,” he said in his email. “What our work does is provide some three-dimensional information at high resolution that helps tie things together.”

Dundas et al reported that the fractures and steep angles found indicate that the ice is cohesive and strong. What’s more, bands and variations in color suggest that the ice contains distinct layers, which could be used to understand changes in Mars’ climate over time.

Because the ice is only visible where surface soil has been removed, the paper says it is likely that ice near the surface is more extensive than detected in this study.

And that could be very important to astronauts on future missions to Mars.

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Cassini Nearing the End, Still Working Hard

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Spiral density wave on Saturn’s moon Janus. (NASA/JPL-Caltech)

As the Cassini mission embarks on its final dive this Friday into Saturn, it will continue taking photos all the way down (or as far as it remains operations.)

We’ve grown accustomed to seeing remarkable images for the mission and the planet, but clearly the show is not over, and perhaps far from it.

This is what NASA wrote describing the image above:

This view  shows a wave structure in Saturn’s rings known as the Janus 2:1 spiral density wave. Resulting from the same process that creates spiral galaxies, spiral density waves in Saturn’s rings are much more tightly wound. In this case, every second wave crest is actually the same spiral arm which has encircled the entire planet multiple times.

This is the only major density wave visible in Saturn’s B ring. Most of the B ring is characterized by structures that dominate the areas where density waves might otherwise occur, but this innermost portion of the B ring is different.

For reasons researchers do not entirely understand, damping of waves by larger ring structures is very weak at this location, so this wave is seen ringing for hundreds of bright wave crests, unlike density waves in Saturn’s A ring.

The image gives the illusion that the ring plane is tilted away from the camera toward upper-left, but this is not the case. Because of the mechanics of how this kind of wave propagates, the wavelength decreases with distance from the resonance. Thus, the upper-left of the image is just as close to the camera as the lower-right, while the wavelength of the density wave is simply shorter.

This wave is remarkable because Janus, the moon that generates it, is in a strange orbital configuration. Janus and Epimetheus (see PIA12602) share practically the same orbit and trade places every four years. Every time one of those orbit swaps takes place, the ring at this location responds, spawning a new crest in the wave.

The distance between any pair of crests corresponds to four years’ worth of the wave propagating downstream from the resonance, which means the wave seen here encodes many decades’ worth of the orbital history of Janus and Epimetheus.

According to this interpretation, the part of the wave at the very upper-left of this image corresponds to the positions of Janus and Epimetheus around the time of the Voyager flybys in 1980 and 1981, which is the time at which Janus and Epimetheus were first proven to be two distinct objects (they were first observed in 1966).

Epimetheus also generates waves at this location, but they are swamped by the waves from Janus, since Janus is the larger of the two moons.

 

The clouds covering the planet itself consist of ammonia ice.  Further down is also some water ice, some ammonium hydrosulfide ice, and further still is ammonia in a gas phase. Some cloud layers are more than 1000 miles thick. (NASA/JPL-Caltech.

This image is from a few months ago, but it certainly puts you there above the deep, deep clouds of Saturn.  False color was used to make the patterns more discernible.

Saturn has some remarkable features in its atmosphere. When the Voyager missions traveled to the planet in the early 1980s, it imaged a hexagon-shaped cloud formation near the north pole. Twenty-five years later, infrared images taken by Cassini revealed the storm was still spinning, powered by jet streams that push it to speeds of about 220 mph (100 meters per second). At 15,000 miles  across, the long-lasting storm could easily contain an Earth or two.

Cassini is now on its last full orbit, to be following by its partial finale.  The final 22 orbits leading to the plunge into the clouds looked like this:

Cassini’s final orbits, in blue, have taken the spacecraft closer to the planet than ever before, and into the space between the rings and the top of the cloud layers. (NASA/JPL-Caltech)

 

And here is a Jet Propulsion Lab video recapping the Cassini mission and describing its Friday rendezvous:

 

(NASA/JPL-Caltech)

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Of White Dwarfs, “Zombie” Stars and Supernovae Explosions

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Artistic view of the aftermath of a supernova explosion, with an unexpected white dwarf remnant. These super-dense but no longer active stars are thought to play a key role in many supernovae explosion. (Copyright Russell Kightley)
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White dwarf stars, the remnant cores of low-mass stars that have exhausted all their nuclear fuel, are among the most dense objects in the sky.
 
Their mass is comparable to that of the sun, while their volume is comparable to that of Earth. Very roughly, this means the average density of matter in a white dwarf would be on the order of 1,000,000 times greater than the average density of the sun.
 
Thought to be the final evolutionary state of stars whose mass is not high enough to become a neutron star — a category that includes the sun and over 97% of the other stars in the Milky Way — they are dim objects first identified a century ago but only in the last decade the subject of broad study.
 
In recent years the white dwarfs have become more and more closely associated with supernovae explosions, though the processes involved remained hotly debated.  A team using the Hubble Space Telescope even captured  before and after images of what is hypothesized to be an incomplete white dwarf supernova.  What was left behind has been described by some as a “zombie star.”
 
Now a team of astronomers led by Stephane Vennes of the Czech Academy of Sciences has detected another zombie white dwarf, LP-40-365 , that they put forward as a far-flung remnant of a long-ago supernova explosion.  This is considered important and unusual because it would represent a first detection of such a remnant long after the supernova conflagration.
 
This dynamic is well captured in an animation accompanying the Science paper that describes the possible remnant.  Here’s the animation and a second-by-second description of what is theorized to have occurred:
 
 
00.0 sec: Initial binary star outside the disk of the Milky Way galaxy. A massive white dwarf accreting
material through an accretion disk from its red giant companion star. The stars orbit around the center of
mass of the binary system.
 
14.6 sec: The white dwarf reaches the Chandrasekhar mass limit and explodes as a bright Type Ia
supernova. However, the explosion is not perfect; a fraction of the white dwarf shoots out like a shrapnel to the left. The binary system disrupts.
 
18.0 sec: The supernova explosion again, at an edge – on view. The shrapnel comes at the viewer and passes by.
 
20.0 sec: After passing by, the remnant flies off towards the disk of the Milky Way towards the spiral arm with the Solar System.
 
24.0 sec : The fast moving remnant from the solar neighborhood as it passes by the stars in our galactic arm, including the Sun. The remnant gets in the reach of our telescopes. (Copyright Sardonicus Pax)

 

A supernova — among the most powerful forces in the universe — occurs when there is a change in the core of a star. A change can occur in two different ways, with both resulting in a thermonuclear explosion.

Type Ia supernova occurs at the end of a single star’s lifetime. As the star runs out of nuclear fuel, some of its mass flows into its core. Eventually, the core is so heavy that it cannot withstand its own gravitational force. The core collapses, which results in the giant explosion of a supernova. The sun is a single star, but it does not have enough mass to become a supernova.

The second type takes place only in binary star systems. Binary stars are two stars that orbit the same point. One of the stars, a carbon-oxygen white dwarf, steals matter from its companion star. Eventually, the white dwarf accumulates too much matter. Having too much matter causes the star to explode, resulting in a supernova.

Type Ia supernovae, which are the result of the complete destruction of the star in a thermonuclear explosion, have a fairly uniform brightness that makes them useful for cosmology. The light emitted by the supernova explosion can be, for a short while at least, as bright as the whole of the Milky Way.

Recently, astronomers have discovered a related form of supernova, called Type Iax, which look like Type Ia, but are much fainter. Type Iax supernovae may be caused by the partial destruction of a white dwarf star in such an explosion. If that interpretation is correct, part of the white dwarf should survive as a leftover object.

And that leftover object is precisely what Vennes et al claim to have found.

They have identified LP 40-365 as an unusual white dwarf with a low mass, high velocity and strange composition of oxygen, sodium and magnesium  – exactly as might be expected for the leftover star from a Type Iax event. Vennes describes the white dwarf remnant his team has detected as a “compact star,” and perhaps the first of its kind in terms of the elements it contains.

The team calculate that the explosion must have occurred between five and 50 million years ago.

 

The two inset images show before-and-after images captured by NASA’s Hubble Space Telescope of Supernova 2012Z in the spiral galaxy NGC 1309, what some call a “zombie star.”. The white X at the top of the main image marks the location of the supernova in the galaxy. A supernova typically obliterates the exploding white dwarf, or dying star.  In 2014, scientists found that this faint supernova may have left behind a surviving portion of the white dwarf star.(NASA,ESA)

In an email exchange, Vennes told me that he has been studying the local white dwarf population for thirty years.

“These compact, dead stars tell us a lot about the “old” Milky Way, how stars were born and how they died,” he wrote.

“Tens of thousands of these white dwarfs have been catalogued over this past century, most of them in the last decade, but we keep an eye on outliers, objects that are out of the norm. We look for exceedingly large velocity, peculiar chemical composition or abnormal mass or radii.

Stephane Vennes, a longtime specialist in white dwarf stars at the Czech Academy of Science.

“The strange case of LP40-365 came unexpectedly, but this was a classic case of serendipity in astronomy. Out of hundreds of targets we observed at the telescope, this one was uniquely peculiar. Fortunately, theorists are very imaginative and the model we adopted to interpret the observed properties of this object were only recently published. Our research on this object was certainly inspired and directed by their theory.”

Vennes says the team was surprised to learn that the white dwarf LP40-365 is relatively bright among its peers and that similar objects did not show up in large-scale surveys such as the Sloan Digital Sky Survey.

“This fact has convinced us that many more similarly peculiar white dwarfs await discovery. We should search among fainter, more distant samples of white dwarfs,” he wrote.

And that search can be done by the European Space Agency’s Gaia astrometric space telescope, with follow-up observations at large telescopes such as the European Southern Observatory’s Very Large Telescope and the Gemini observatory in Chile.

“It is also likely that our adopted model involving a subluminous {faint} Type Ia supernova will be modified or even superseded by teams of theorists coming up with new ideas. But we remain confident that these new ideas would still involve a cataclysmic event on the scale of a supernova.”

Here is another animated version of the cataclysm described in the paper: 

An ultra-massive and compact dead star, or white dwarf, (shown as a small white star) is accreeting matter from its giant companion (the larger red star). The material escapes from the giant and forms an accretion disk around the white dwarf.
Once enough material is accreted onto the white dwarf, a violent thermonuclear runaway tears it apart and destroys the entire system. The giant star and the surviving fragment of the white dwarf are flung into space at tremendous speeds. The surviving white dwarf shrapnel hurtles towards our region of the galaxy, where its radiation is detected by ground based telescopes. (Copyright Russell Kightley)

 

A supernova burns for only a short period of time, but it can tell scientists a lot about the universe.

One kind of supernova has shown scientists that we live in an expanding universe, one that is growing at an ever increasing rate.

Scientists also have determined that supernovas play a key role in distributing elements throughout the universe. When the star explodes, it shoots elements and debris into space. Many of the elements we find here on Earth are made in the core of stars.

These elements travel on to form new stars, planets and everything else in the universe — making white dwarfs and supernovae essential to the process that ultimately led to life.

 

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