Posted on by Jon Voisey

Finding the Failed Supernovae

Recipe for a pair instability supernova. It is hypothesised that in extremely massive stars, gamma rays radiating from the core become so energetic that they can undergo pair production after interaction with a nucleus. Essentially, the gamma ray creates a paired particle and antiparticle (commonly an electron and a positron). The loss of radiation pressure as gamma rays convert to particles results in gravitational collapse of the star's core - and kaboom! Credit: chandra.harvard.edu

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When high mass stars end their lives, they explode in monumental supernovae. But, when the most massive of these monsters die, theory has predicted that they may not even reveal as much as a whimper as their massive cores implode. Instead, the implosion occurs so quickly, that the rebound and all photons created during it, are immediately swallowed into the newly formed black hole. Estimates have suggested that as much as 20% of stars that are massive enough to form supernovae collapse directly into a black hole without an explosion. These “failed supernovae” would simply disappear from the sky leaving such predictions seemingly impossible to verify. But a new paper explores the potential for neutrinos, subatomic particles that rarely interact with normal matter, could escape during the collapse, and be detected, heralding the death of a giant.

Presently, only one supernova has been detected by its neutrinos. This was supernova 1987a, a relatively close supernova which occurred in the Large Magellanic Cloud, a satellite galaxy to our own. When this star exploded, the neutrinos escaped the surface of the star and reached detectors on Earth three hours before the shockwave reached the surface, producing a visible brightening. Yet despite the enormity of the eruption, only 24 neutrinos (or more precisely, electron anti-neutrinos), were detected between three detectors.

The further away an event is, the more its neutrinos will be spread out, which in turn, decreases the flux at the detector. With current detectors, the expectation is that they are large enough to detect supernovae events around a rate of 1-3 per century all originating from within the Milky Way and our satellites. But as with most astronomy, the detection radius can be increased with larger detectors. The current generation uses detectors with masses on the order of kilotons of detecting fluid, but proposed detectors would increase this to megatons, pushing the sphere of detectability to as much as 6.5 million light years, which would include our nearest large neighbor, the Andromeda galaxy. With such enhanced capabilities, detectors would be expected to find neutrino bursts on the order of once per decade.

Assuming the calculations are correct and that 20% of supernova implode directly, this means that such gargantuan detectors could detect 1-2 failed supernovae per century. Fortunately, this is slightly enhanced due to the extra mass of the star, which would make the total energy of the event higher, and while this wouldn’t escape as light, would correspond to an increased neutrino output. Thus, the detection sphere could be pushed out to potentially 13 million lightyears, which would incorporate several galaxies with high rates of star formation and consequently, supernoave.

While this puts the potential for detections of failed supernovae on the radar, a bigger problem remains. Say neutrino detectors record a sudden burst of neutrinos. With typical supernovae, this detection would be quickly followed with the optical detection of a supernova, but with a failed supernova, the followup would be absent. The neutrino burst is the beginning and end of the story, which could not initially positively define such an event as different from other supernovae, such as those that form neutron stars.

To tease out the subtle differences, the team modeled the supernovae to examine the energies and durations involved. When comparing failed supernovae to ones forming neutron stars, they predicted that the failed supernovae neutrino bursts would have shorter durations (~1 second) than ones forming neutron stars (~10 seconds). Additionally, the energy imparted in the collision that makes up the detection would be higher for failed supernovae (up to 56 MeV vs 33 MeV). This difference could potentially discriminate between the two types.

Posted on by Nancy Atkinson

10-Year-Old Girl Discovers a Supernova

A before and after animation of Supernova 2010lt. Credit: Dave Lane

A ten-year old girl from Canada has discovered a supernova, making her the youngest person ever to find a stellar explosion. The Royal Astronomical Society of Canada announced the discovery by Kathryn Aurora Gray of Fredericton, New Brunswick, (wonderful middle name!) who was assisted by astronomers Paul Gray and David Lane. Supernova 2010lt is a magnitude 17 supernova in galaxy UGC 3378 in the constellation of Camelopardalis, as reported on IAU Electronic Telegram 2618. The galaxy was imaged on New Year’s Eve 2010, and the supernova was discovered on January 2, 2011 by Kathryn and her father Paul.

Continue reading “10-Year-Old Girl Discovers a Supernova”

Posted on by Nancy Atkinson

‘Ring’ in the Holidays with New Hubble Bubble Image

SNR 0509 is the visible remnant of a powerful stellar explosion in the Large Magellanic Cloud. Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA). Acknowledgement: J. Hughes (Rutgers University)

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From a Hubble/ESA press release:

A festive, delicate ring –photographed by the Hubble Space Telescope — appears to float serenely in the depths of space, but this apparent calm hides an inner turmoil. The gaseous envelope formed as the expanding blast wave and ejected material from a supernova tore through the nearby interstellar medium. Called SNR B0509-67.5 (or SNR 0509 for short), the bubble is the visible remnant of a powerful stellar explosion in the Large Magellanic Cloud (LMC), a small galaxy about 160,000 light-years from Earth.

Ripples seen in the shell’s surface may be caused either by subtle variations in the density of the ambient interstellar gas, or possibly be driven from the interior by fragments from the initial explosion. The bubble-shaped shroud of gas is 23 light-years across and is expanding at more than 18 million km/h.

Astronomers have concluded that the explosion was an example of an especially energetic and bright variety of supernova. Known as Type Ia, such supernova events are thought to result when a white dwarf star in a binary system robs its partner of material, taking on more mass than it is able to handle, so that it eventually explodes.

Hubble’s Advanced Camera for Surveys observed the supernova remnant on 28 October 2006 with a filter that isolates light from the glowing hydrogen seen in the expanding shell. These observations were then combined with visible-light images of the surrounding star field that were imaged with Hubble’s Wide Field Camera 3 on 4 November 2010.

With an age of about 400 years, the supernova might have been visible to southern hemisphere observers around the year 1600, although there are no known records of a “new star” in the direction of the LMC near that time. A much more recent supernova in the LMC, SN 1987A, did catch the eye of Earth viewers and continues to be studied with ground- and space-based telescopes, including Hubble.

Posted on by Nancy Atkinson

WISE Captures an Infrared Shock Wave

This oddly colorful nebula is the supernova remnant IC 443 as seen by WISE. Image credit: NASA/JPL-Caltech/UCLA

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From a JPL press release:

A circular rainbow appears like a halo around an exploded star in this new view of the IC 443 nebula from NASA’s Wide-field Infrared Survey Explorer, or WISE.

When massive stars die, they explode in tremendous blasts, called supernovae, which send out shock waves. The shock waves sweep up and heat surrounding gas and dust, creating supernova remnants like the one pictured here. The supernova in IC 443 happened somewhere between 5,000 and 10,000 years ago.

In this WISE image, infrared light has been color-coded to reveal what our eyes cannot see. The colors differ primarily because materials surrounding the supernova remnant vary in density. When the shock waves hit these materials, different gases were triggered to release a mix of infrared wavelengths.

The supernova remnant’s northeastern shell, seen here as the violet-colored semi-circle at top left, is composed of sheet-like filaments that are emitting light from iron, neon, silicon and oxygen gas atoms and dust particles heated by a fast shock wave traveling at about 100 kilometers per second, or 223,700 mph.

The smaller southern shell, seen in bright bluish colors, is constructed of clumps and knots primarily emitting light from hydrogen gas and dust heated by a slower shock wave traveling at about 30 kilometers per second, or 67,100 miles per hour. In the case of the southern shell, the shock wave is interacting with a nearby dense cloud. This cloud can be seen in the image as the greenish dust cutting across IC 443 from the northwest to southeast.

IC 443 can be found near the star Eta Geminorum, which lies near Castor, one of the twins in the constellation Gemini.

Posted on by Jon Voisey

Will V445 Puppis Become a Ia Supernova?

As the “V” in the designation of V445 Puppis indicates, this star was a variable star located in the constellation of Puppis. It was a fairly ordinary periodic variable, although with a rather complex light curve, but still showing a distinct periodicity of about fifteen and a half hours. It wasn’t especially bright, yet something seemed to tug at my memory regarding the star’s name as I scanned through articles to write on. Just over a year ago, Nancy wrote a post on V445 Puppis stating it’s a supernova just waiting to happen. A new article challenges this claim.

In December of 2000, V445 Puppis underwent an unusual nova. It was first noticed on December 30th, but archival records showed the eruption began in early November of that year and reached a peak brightness on November 29th. The system was known to be a binary star system with a shared envelope in which the primary star was a white dwarf and thus, a nova was the most readily available explanation.

However, this wasn’t a normal nova. Spectroscopic observations early the next year showed the ejecta lacked the helium emission seen in classical novae in which hydrogen piles up on a white dwarf surface until it undergoes fusion into helium. Instead, astronomers saw lines of iron, calcium, carbon, sodium, and oxygen expanding at nearly 1,000 km/sec. This fit better with a proposed type of explosion where, instead of hydrogen collecting on the dwarf’s surface, it was helium and the eruption seen was a helium flash in which it was helium that underwent fusion. Slowly the star faded, and debris from the eruption cooled to form dust. Today, the star itself is completely obscured in the visible portion of the spectrum.

The 2009 paper by Woudt, Steeghs, and Karowska that Nancy cited, suggested accretion might continue until the white dwarf passed the Chandrasekhar limit and exploded as a type Ia supernova. However, the authors of the new paper, led by V. P. Goranskij at Moscow University, say that this 2000 detonation has effectively ruled out that possibility because an explosion of that magnitude would likely destroy the envelope of the donor star. Their evidence for this is the very same structure Woudt noted in his paper (shown above).

While the structure looks to be bipolar in nature, other observations have suggested that there is an additional component along the line of sight and that the structure is more of a doughnut shape. In this case, the total amount of material lost is higher than originally anticipated and must have come from from the envelope of the companion star. Additionally, observations in wavelengths able to pierce the dust have been unable to resolve a strong stellar source which suggests that the donor star’s envelope has been largely blown away as well. Additionally, this large and rapid loss of mass from the system may have broken the gravitational bond between the two stars and allowed the giant star to be ejected from the system, which would also preclude the possibility of a supernova in the future.

The conclusion is that V445 Puppis is not a candidate for a supernova of any type in the future. It’s own premature fireworks have likely destroyed whatever chance it may have had for an even grander show in the future.

Posted on by Mike Simonsen

Do Puny White Dwarfs Make Wimpy Supernovae?

The binary star system J0923+3028 consists of two white dwarfs: a visible star 23 percent as massive as our Sun and about four times the diameter of Earth, and an unseen companion 44 percent of the Sun's mass and about one Earth-diameter in size. The stars will spiral in toward each other and merge in about 100 million years. (Credit: Clayton Ellis (CfA))

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Based on results from a radial velocity survey, Warren Brown, (Smithsonian Astrophysical Observatory) and his team have placed a few more pieces into the supernova puzzle.

Supernovae come in many flavors. There are Type Ia, the “standard candles” everyone has heard of; and there are Type Ib and Ic, which also involve binary systems. We also have Type II supernovae that are believed to be the core collapse of single, super-massive stars. There are also super-luminous supernovae, which may be the explosive conversion of a neutron star into a quark star, and finally the weak-kneed cousins of the bunch, the under-performing underluminous supernovae.

Underluminous supernovae are a rare type of supernova explosion 10–100 times less luminous than a normal SN Type Ia and eject only 20% as much matter. Brown and his team have been investigating the connection between underluminous supernovae and merging pairs of white dwarfs.

In the 1980s, on the basis of our theoretical understanding of stellar and binary evolution it was predicted that many close double white dwarfs would exist. However, it was not until 1988 that the first one was actually discovered.

The way to find close double white dwarfs is to take high resolution spectra of the H-alpha absorption line of a white dwarf at several different times and look for variation that is caused by the orbital motion of the white dwarf around an unseen (dimmer) companion. The first systematic searches were not very unsuccessful. Only one system was found. Then, during the 1990s, Tom Marsh and collaborators concentrated their search on low-mass white dwarfs, which, based on current theories, could _only_ be formed in a binary system. In this way a dozen more systems were found.

Extremely low mass (ELM) white dwarfs (WDs) with less than 0.3 solar masses are the remnants of stars that never ignited helium in their cores. The Universe is not old enough to have produce ELM WDs by single star evolution. Therefore, ELM WDs must undergo significant mass loss sometime in their evolution. Producing WDs with 0.2 solar masses most likely requires compact binary systems.

“These white dwarfs have gone through a dramatic weight loss program,” said Carlos Allende Prieto, an astronomer at the Instituto de Astrofisica de Canarias in Spain and a co-author of the study. “These stars are in such close orbits that tidal forces, like those swaying the oceans on Earth, led to huge mass losses.”

Observational data for ELM WDs is pretty hard to come by because of their rarity. For example, of the 9316 WDs identified in the Sloan Digital Sky Survey, less than 0.2% have masses below 0.3 solar.

Half of the pairs discovered by Brown and collaborators are merging and might explode as supernovae in 100 million years or more.

“We have tripled the number of known, merging white-dwarf systems,” said Smithsonian astronomer and co-author Mukremin Kilic. “Now, we can begin to understand how these systems form and what they may become in the near future.” Unlike normal white dwarfs made of carbon and oxygen, these are made almost entirely of helium.

“The rate at which our white dwarfs are merging is the same as the rate of under-luminous supernovae – about one every 2,000 years,” explained Brown. “While we can’t know for sure whether our merging white dwarfs will explode as under-luminous supernovae, the fact that the rates are the same is highly suggestive.”

At least 25% of these ELM WDs belong to the old thick disk and halo components of the Milky Way. This helps astronomers know where to look for underluminous SNe and where they are unlikely to find them, if the models are correct. If merging ELM WD systems are the progenitors of underluminous SNe, the next generation of surveys such as the Palomar Transient Factory, Pan-STARRS, Skymapper, and the Large Synoptic Survey Telescope should find them amongst the older populations of stars in both elliptical and spiral galaxies.

The papers announcing their find are available online at: http://arxiv.org/abs/1011.3047 and http://arxiv.org/abs/1011.3050.

Posted on by Jon Voisey

Galaxy Zoo Searches for Supernovae

Aside from categorizing galaxies, another component of the Galaxy Zoo project has been asking participants to identify potential supernovae (SNe). The first results are out and have identified “nearly 14,000 supernova candidates from [Palomar Transient Factory, (PTF)] were classified by more than 2,500 individuals within a few hours of data collection.”

Although the Galaxy Zoo project is the first to employ citizens as supernova spotters, the background programs have long been in place but were generating vast amounts of data to be processed. “The Supernova Legacy Survey used the MegaCam instrument on the 3.6m Canada-France-Hawaii Telescope to survey 4 deg2” every few days, in which “each square degree would typically generate ~200 candidates for each night of observation.” Additionallly, “[t]he Sloan Digital Sky Survey-II Supernova Survey used the SDSS 2.5m telescope to survey a larger area of 300 deg2” and “human scanners viewed 3000-5000 objects each night spread over six scanners”.

To ease this burden, the highly successful Galaxy Zoo implemented a Supernova Search in which users would be directed through a decision tree to help them determine what computer algorithms were proposing as transient events. Each image would be viewed and decided on by several participants increasing the likelihood of a correct appraisal. Also, “with a large number of people scanning candidates, more candidates can be examined in a shorter amount of time – and with the global Zooniverse (the parent project of Galaxy Zoo) user base this can be done around the clock, regardless of the local time zone the science team happens to be based in” allowing for “interesting candidates to be followed up on the same night as that of the SNe discovery, of particular interest to quickly evolving SNe or transient sources.”

To identify candidates for viewing, images are taken using the 48 inch Samuel Oschin telescope at the
Palomar Observatory. Images are then calibrated to correct instrumental noise and compared automatically to reference images. Those in which an object appears with a change greater than five standard deviations from the general noise are flagged for inspection. While it may seem that this high threshold would eliminate other events, the Supernova Legacy Survey, starting with 200 candidates per night, would only end up identifying ~20 strong candidates. As such, nearly 90% of these computer generated identifications were spurious, likely generated by cosmic rays striking the detector, objects within our own solar system, or other such nuisances and demonstrating the need for human analysis.

Still, the PTF identifies between 300 and 500 candidates each night of operation. When exported to the Galaxy Zoo interface, users are presented with three images: The first is the old, reference image. The second is the recent image, and the third is the difference between the two, with brightness values subtracted pixel for pixel. Stars which didn’t change brightness would be subtracted to nothing, but those with a large change (such as a supernova), would register as a still noticeable star.

Of course, this method is not flawless, which also contributes to the false positives from the computer system that the decision tree helps weed out. The first question (Is there a candidate centered in the crosshairs of the right-hand [subtracted] image?) eliminates misprocessing by the algorithm due to misalignment. The second question (Has the candidate itself subtracted correctly?) serves to drop stars that were so bright, they saturated the CCD, causing odd errors often resulting in a “bullseye” pattern. Third (Is the candidate star-like and approximately circular?), users eliminate cosmic ray strikes which generally only fill one or two pixels or leave long trails (depending on the angle at which they strike the CCD). Lastly, users are asked if “the candidate centered in a circular host galaxy?” This sets aside identifications of variable stars within our own galaxy that are not events in other galaxies as well as supernovae that appear in the outskirts of their host galaxies.

Each of these questions is assigned a number of positive or negative “points” to give an overall score for the identification. The higher the score, the more likely it is to be a true supernova. With the way the structure is set up, “candidates can only end up with a score of -1, 1 or 3 from each classification, with the most promising SN candidates scored 3.” If enough users rank an event with the appropriate score, the event is added to a daily subscription sent out to interested parties.

To confirm the reliability of identifications, the top 20 candidates were followed up spectroscopically with the 4.2m William Herschel Telescope. Of them, 15 were confirmed as SNe, with 1 cataclysmic variable, and 4 remain unknown. When compared to followup observations from the PTF team, the Galaxy Zoo correctly identified 93% of supernova that were confirmed spectroscopically from them. Thus, the identification is strong and this large volume of known events will certainly help astronomers learn more about these events in the future.

If you’d like to join, head over to their website and register. Presently, all supernovae candidates have been processed, but the next observing run is coming up soon!

Posted on by Tammy Plotner

New Supernova Lights Up Leo

A new supernova? Darn right. Lighting up Leo? Well… not without some serious visual aid, but the fact that someone out there is watching and has invited us along for the ride is mighty important. And just who might that someone be? None other than Tim Puckett.

Less than 24 hours ago, the American Association of Variable Star Observer’s Report #222 stated:

“Bright Supernova in UGC 5189A: SN 2010jl
November 5, 2010

We have been informed by Tim Puckett and by the Central Bureau for Astronomical Telegrams (CBET 2532, Daniel W. E. Green, Ed.) of the discovery of a bright supernova in UGC 5189A by J. Newton and Puckett, Portal, AZ, on November 3.52 UT at unfiltered magnitude 13.5. Confirming images (limiting magnitude 19.1) by Puckett on Nov. 4.50 UT showed the object at magnitude 12.9.

Spectroscopic observations (CBET 2536, Daniel W. E. Green, Ed.) by S. Benetti and F. Bufano, Istituto Nazionale di Astrofisica, Osservatorio Astronomico di Padova, on behalf of a larger collaboration, and by J. Vinko, University of Szeged, G. H. Marion, Harvard-Smithsonian Center for Astrophysics and University of Texas, T. Pritchard, Pennsylvania State University, and J. C. Wheeler and E. Chatzopoulos, University of Texas, show that SN 2010jl is a type-IIn supernova. Vinko et al. also report that simultaneous measurements with Swift/UVOT in the ultraviolet bands confirm that the transient is ultraviolet-bright, as expected for young, interacting supernovae.

Coordinates: 09 42 53.33 +09 29 41.8 (J2000.0) This position is 2.4″ east and 7.7″ north of the center of UGC 5189A. This AAVSO Special Notice was prepared by Elizabeth O. Waagen.”


While magnitude 12-12.9 isn’t unaided eye bright by a long shot, it’s well within the reach of most of today’s backyard telescopes. The image you see here on the right is of UGC 5189A before the event and the lefthand image was taken at the time of the supernova report. Visually the SN event outshines the galaxy! While chasing a faint supernova event might not be everyone’s cup of tea, Mr. Puckett’s devotion is absolutely legendary and I strongly encourage you to have a look if you have the the tools and talent.

So many supernovae… So little time!

Posted on by Jon Voisey

What was SN 1961V?

NGC 1058. Image credit: Bob Ferguson and Richard Desruisseau/Adam Block/NOAO/AURA/NSF
NGC 1058. Image credit: Bob Ferguson and Richard Desruisseau/Adam Block/NOAO/AURA/NSF

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Up there in the sky! It’s a supernova! It’s a Luminous Blue Variable eruption! It’s…. well, we’re not sure….

In July of 1961, a star in the spiral galaxy NGC 1058 blew up, but in a very odd fashion. The time to reach its peak brightness was several months as well as a slow decline including a three year plateau. Narrow spectral lines revealed a slow expansion velocity of 2,000 km sec-1. Some proposed it was an unusual supernova. Others claimed it was an especially energetic eruption of a Luminous Blue Variable (LBV) star like Eta Carinae. The infamous Fritz Zwicky called it a “Type V Supernova” which meant a supernova in name only, but could be anything as it was simply an “impostor”. For nearly 50 years, astronomers have been trying to sort out what this supernova impostor truly was.

One front on which much of the effort has focused is on the nature of the star before the explosion. The host galaxy is a beautiful face on spiral galaxy and was a tempting target for many observations well before the eruption. This has allowed astronomers to use archival images to determine properties of the parent star. And what a whopper it was. The star had an absolute magnitude near -12! Even Eta Carinae, one of the most massive stars currently known, only has an absolute magnitude of around -5.5. This extreme luminosity led astronomers towards early estimates for its mass to be as much as a staggering 2,000 M☉! While this is certainly incorrect, it still reveals just how massive SN 1961V’s progenitor truly was. Most estimates now put it in the range of 100 – 200 M☉.

A key difference between a supernova and an eruption is the remnant. In the case of a supernova, it is expected that the result would be a neutron star or black hole. If the object were an eruption, even a large one, the star would remain intact. In this vein, many astronomers have also attempted to inspect the remnant. However, due to the shell of gas and dust created in either scenario, imaging the objects has proven to be a challenge. While prior to the event, the culprit stuck out like a sore thumb, the remnant is lost in a haze of other stars.

Numerous telescopes have been aimed at the region to attempt to ferret out the leftovers including the powerful Hubble, but many attempts have remained inconclusive. Recently, the Spitzer Space telescope was employed to study the region, and although not intended for studying individual stars, its infrared vision can allow it to pierce the veil of dust and potentially find the source responsible. If there is still an intense IR source, it would mean the star survived, and the supernova truly was an impostor.

This attempt at identification was recently undertaken by a team of astronomers from Ohio State University, led by Christopher Kochanek. Upon inspection, the team was unable to conclusively identify a source with sufficient intensity as to be a survivor of the SN 1961V event. As such, the team concluded that the event Zwicky defined as a “supernova impostor” was a “‘supernova impostor’ impostor”.

The team compared it to another recent supernova, SN 2005gl, which also had a supermassive progenitor and was observed prior to detonation. Previous studies of this supernova suggested that, just prior to the explosion itself, the star underwent a heavy phase of mass loss. If a similar scenario occurred in 1961V, it could explain the unusual expansion velocity. During this time, the star may quake ferociously, imitating LBV eruptions which could explain the pre-nova plateau.

While this comparison relies on a single strongly similar case, it underscores the need “that studies of SN progenitors should evolve from simple attempts to obtain a single snapshot of the star to monitoring their behavior over their final years.” Hopefully, future studies and observations will provide better theoretical simulations and the numerous large surveys will provide sufficient data on stars prior to eruption to better constrain the behavior of these monsters.

Posted on by Jon Voisey

Poor in one, Rich in another

Tycho's Supernova Remnant. Credit: Spitzer, Chandra and Calar Alto Telescopes.

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Just over three years ago, I wrote a blog post commemorating the 50th anniversary of one of the most notable papers in the history of astronomy. In this paper, Burbidge, Burbidge, Fowler, and Hoyle laid out the groundwork for our understanding of how the universe builds up heavy elements.

The short version of the story is that there are two main processes identified: The slow (s) process and the rapid (r) process. The s-process is the one we often think about in which atoms are slowly bombarded with protons and neutrons, building up their atomic mass. But as the paper pointed out, this often happens too slowly to pass roadblocks to this process posed by unstable isotopes which don’t last long enough to catch another one before falling back down to lower atomic number. In this case, the r-process is needed in which the flux of nucleons is much higher in order to overcome the barrier.

The combination of these two processes has done remarkably well in matching observations of what we see in the universe at large. But astronomers can never rest easily. The universe always has its oddities. One example is stars with very odd relative amounts of the elements built up by these processes. Since the s-process is far more common, they’re what we should see primarily, but in some stars, such as SDSS J2357-0052, there exists an exceptionally high concentration of the rare r-process elements. A recent paper explores this elemental enigma.

As the designation implies, SDSS J2357-0052’s uniqueness was discovered by the Sloan Digital Sky Survey (SDSS). The survey uses several filters to image fields of stars at different wavelengths. Some of the filters are chosen to lie in wavelength ranges in which there are well known absorption lines for elements known to be tracers of overall metallicity. This photometric system allowed an international team of astronomers, led by Wako Aoki of the National Astronomical Observatory in Tokyo, to get a quick and dirty view of the metal content of the stars and choose interesting ones for followup study.

These followup observations were done with high resolution spectroscopy and showed that the star had less than one one-thousandth the amount of iron that the Sun does ([Fe/H] = -3.4), placing it among the most metal poor stars ever discovered. However, iron is the end of the elements produced by the s-process. When going beyond that atomic number, the relative abundances drop off very quickly. While the drop off in SDSS J2357-0052 was still steep, it wasn’t near as dramatic as in most other stars. This star had a dramatic enhancement of the r-process elements.

Yet this wasn’t exceptional in and of itself. Several metal poor stars have been discovered with such r-process enhancements. But none coupled with such an extreme deficiency of iron. The implication of this combination is that this star was very close to a supernova. The authors suggest two scenarios that can explain the observations. In the first, the supernova occurred before the star formed, and SDSS J2357-0052 was formed in the immediate vicinity before the enhanced material would be able to disperse and mix into the interstellar medium. The second is that SDSS J2357-0052 was an already formed star in a binary orbit with a star that became a supernova. If the latter case is true, it would likely give the smaller star a large “kick” as the mass holding the system would change dramatically. Although no exceptional radial velocity was detected for SDSS J2357-0052, the motion (if it exists) could be in the plane of the sky requiring proper motion studies to either confirm or refute this possibility.

The authors also note that the first star with somewhat similar characteristics (although not as extreme), was discovered first in the outer halo where the likelihood of the necessary supernova occurring is low. As such, it is more likely that that star was ejected in such a process establishing some credibility for the scenario in general, even if not the case for SDSS J2357-0052.