A "super star cluster", Westerlund 1, which is about 16,000 light-years from Earth. It can be found in the southern constellation of Ara. The picture was taken from the European Southern Observatory's VLT Survey Telescope. Credit: ESO/VPHAS+ Survey/N. Wright
The faint green glow you see in that picture is not an early harbringer of Hallowe’en spooks. It’s hydrogen gas clouds found recently nearby W26, a future supernova in the star cluster Westerlund 1.
The European Southern Observatory’s VLT Survey Telescope in Chile spotted the hydrogen in the cluster, which has hundreds of huge stars that are only believed to be a few million years old. (Our solar system, by comparison, is about 4.5 billion years old.)
“Such glowing clouds around massive stars are very rare, and are even rarer around a red supergiant— this is the first ionised nebula discovered around such a star,” the European Southern Observatory stated.
“W26 itself would be too cool to make the gas glow; the astronomers speculate that the source of the ionizing radiation may be either hot blue stars elsewhere in the cluster, or possibly a fainter, but much hotter, companion star to W26.”
Funny enough, the nebula that surrounds the red supergiant is similar to the one surrounding SN1987A, a star that exploded as a fairly bright supernova in 1987. “Studying objects like this new nebula around W26 will help astronomers to understand the mass loss processes around these massive stars, which eventually lead to their explosive demise,” ESO added.
One of the first photos of the possible new supernova in the nearby galaxy M74 taken by the Italian Supernova Search Project. The object is located 93" east and 135" south of the galaxy's center. Click to learn more about the search group. Credit: Fabio Martinelli
I love this galaxy. Not only does M74display a near perfect spiral form but if this latest supernova is the third to “go boom” in the galaxy in just 11 years. The new object, designated PSN J01364816+1545310, was discovered blazing near 12.4 magnitude by the Lick Observatory Supernova Search at Lick Observatory near San Jose, Calif. “PSN” stands for “possible supernova” and the long string of numbers give the object’s position in the sky using the celestial equivalents of latitude and longitude.
Update: The supernova has now been confirmed, and is now officially named SN 2013ej.
Supernova 2013ej, taken remotely on July 29, 2013 from iTelescope Network using the Siding Spring Observatory. Credit: Ernesto Guido and Nick Howes/Remanzacco Observatory.
M74 is a classic spiral galaxy with arms that appear to unwind from a bright, star-packed nucleus. Located 32 million light years away in the constellation Pisces, M74 contains about 100 billion stars. The spiral arms are dotted with dense star clusters and pink clouds of fluorescing hydrogen gas. Credit: Jim Misti
The Lick search uses a fully robotic or automated 30-inch (76 cm) telescope dedicated to scanning the skies for new supernovae. It nailed M74’s latest exploding star on July 25. Two previous supernovae flared in the galaxy – SN 2002apand SN 2003gd– and rose to 12th and 13th magnitude respectively before fading away into obscurity.
Size comparison of our Milky Way spiral galaxy with M74. The Milky Way measures about 100,000 light years across; M74 about 30,000. Credit: NASA (left) and Jim Misti
Three’s the charm as they say. A team of astronomers using a spectrograph at the Faulkes Telescope South at Siding Spring, Australia teased apart the supernova’s light and now know exactly what blew up. It appears our newcomer was originally a supergiant star at least 8 times as massive as the sun. After a relatively brief lifetime measured in the millions of years, the supergiant gobbled up the last of its fuel. With the gas gauge on “empty” and no new energy being produced in the core to hold back the force of gravity, the star imploded, sending a shockwave rocketing back in the opposite direction that tore it to bits.
When a massive star runs out of nuclear fuel in its core, the energy that has prevented the force of gravity from crushing it is gone. Gravity finally gains the upper hand causing the star to implode. A rebounding shock wave blows it to bits. Sometime a city-sized, dense stellar remnant called a neutron star remains after the blast. Credit: ESO
Called a Type II supernova explosion, the blast hurtles star stuff into space at up to 45,000 miles per second (70,000 km/sec). More amazing, a powerful supernova explosion can release as much energy as the sun during its entire 10 billion year lifetime. No wonder even small telescopes can spot these cataclysmic events from millions of light years away!
The galaxy M74, the 74th entry in 18th century astronomer Charles Messier’s catalog, is found about 1.5 degrees east-northeast of the star Eta Piscium just to the right of the small constellation Aries the Ram. The map shows the sky around 1 a.m. tomorrow morning facing east. Stellarium
As additional photos and measurements come in, amateur astronomers with 8-inch and larger telescopes will have no problem spying the supernova once the last quarter moon departs the vicinity. It’s located 93″ (1.5′) east and 135″ (more than 2′) southeast of the galaxy’s core. The map and photo will help you track it down.
This map measures only about 1/2-degree wide and shows the galaxy up close with the supernova marked SN. Selected star magnitudes from the AAVSO are shown to help you navigate to the object as well as estimate its brightness. North is up, west to the right. Map created with Chris Marriott’s SkyMap software
While M74 is relatively bright and appears spectacular in long-exposure photos, it looks like a large, dim featureless glow in smaller telescopes. Be patient and take your time to “star hop” to the supernova using the more detailed map. Matter of fact, you may want to wait until Tuesday morning or later to look. That’s when the waning moon will finally depart the area. Let’s hope our new guest remains bright.
Good luck meeting the latest star to mark the end of its life with the biggest blowout of all. For more information and photos, stop by Dave Bishop’s Latest Supernovae site.
* This article was updated at 6:30 pm CDT on 7/28/13
Mu Cephei (arrowed) in the constellation Cepheus the King. (Photo & graphic by author).
Quick, what’s the reddest star visible to the naked eye?
Depending on your sky conditions, your answer may well be this week’s astronomical highlight.
Mu Cephei, also known as Herschel’s Garnet Star, is a ruddy gem in the constellation Cepheus near the Cygnus/Lacerta border. A variable star ranging in brightness by a factor of about three-fold from magnitudes 5.0 to 3.7, Mu Cephei is low to the northeast for mid-northern latitude observers in July at dusk, and will be progressively higher as summer wears on. Continue reading “Seeing Red: Hunting Herschel’s Garnet Star”
This "SWASI" phenomenon is an analogue of the SASI instability occurring in the supernova core, but it is one million times smaller and about one hundred times slower than its astrophysical counterpart. (Image copyrights: Thierry Foglizzo, Laboratoire AIM Paris-Saclay, CEA)
It’s one of the most intense and violent of all events in space – a supernova. Now a team of researchers at the Max Planck Institute for Astrophysics have been taking a very specialized look at the formation of neutron stars at the center of collapsing stars. Through the use of sophisticated computer simulations, they have been able to create three-dimensional models which show the physical effects – intense and violent motions which occur when stellar matter is drawn inward. It’s a bold, new look into the dynamics which happen when a star explodes.
As we know, stars which have eight to ten times the mass of the Sun are destined to end their lives in a massive explosion, the gases blown into space with incredible force. These cataclysmic events are among the brightest and most powerful events in the Universe and can outshine a galaxy when they occur. It is this very process which creates elements critical to life as we know it – and the beginnings of neutron stars.
Neutron stars are an enigma unto themselves. These highly compact stellar remnants contain as much as 1.5 times the mass of the Sun, yet are compressed to the size of a city. It is not a slow squeeze. This compression happens when the stellar core implodes from the intense gravity of its own mass… and it takes only a fraction of a second. Can anything stop it? Yes. It has a limit. Collapse ceases when the density of the atomic nuclei is exceeded. That’s comparable to around 300 million tons compressed into something the size of a sugar cube.
Studying neutron stars opens up a whole new dimension of questions which scientists are keen to answer. They want to know what causes stellar disruption and how can the implosion of the stellar core revert to an explosion. At present, they theorize that neutrinos may be a critical factor. These tiny elemental particles are created and expelled in monumental numbers during the supernova process and may very well act as heating elements which ignite the explosion. According to the research team, neutrinos could impart energy into the stellar gas, causing it to build up pressure. From there, a shock wave is created and as it speeds up, it could disrupt the star and cause a supernova.
As plausible as it might sound, astronomers aren’t sure if this theory could work or not. Because the processes of a supernova cannot be recreated under laboratory conditions and we’re not able to directly see into the interior of a supernovae, we’ll just have to rely on computer simulations. Right now, researchers are able to recreate a supernova event with complex mathematical equations which replicate the motions of stellar gas and the physical properties which happen at the critical moment of core collapse. These types of computations require the use of some of the most powerful supercomputers in the world, but it has also been possible to use more simplified models to get the same results. “If, for example, the crucial effects of neutrinos were included in some detailed treatment, the computer simulations could only be performed in two dimensions, which means that the star in the models was assumed to have an artificial rotational symmetry around an axis.” says the research team.
With the support of the Rechenzentrum Garching (RZG), scientists were able to create in a singularly efficient and fast computer program. They were also given access to most powerful supercomputers, and a computer time award of nearly 150 million processor hours, which is the greatest contingent so far granted by the “Partnership for Advanced Computing in Europe (PRACE)” initiative of the European Union, the team of researchers at the Max Planck Institute for Astrophysics (MPA) in Garching could now for the first time simulate the processes in collapsing stars in three dimensions and with a sophisticated description of all relevant physics.
“For this purpose we used nearly 16,000 processor cores in parallel mode, but still a single model run took about 4.5 months of continuous computing”, says PhD student Florian Hanke, who performed the simulations. Only two computing centers in Europe were able to provide sufficiently powerful machines for such long periods of time, namely CURIE at Très Grand Centre de calcul (TGCC) du CEA near Paris and SuperMUC at the Leibniz-Rechenzentrum (LRZ) in Munich/Garching.
Turbulent evolution of a neutron star for six moments (0.154, 0.223, 0.240, 0.245, 0.249 and 0.278 seconds) after the beginning of the neutron star formation in a threedimensional computer simulation. The mushroom-like bubbles are characteristic of “boiling” neutrino-heated gas, whereas simultaneously the “SASI” instability causes wild sloshing and rotational motions of the whole neutrino-heated layer (red) and of the enveloping supernova shock (blue) . (Images by Elena Erastova and Markus Rampp, RZG)Given several thousand billion bytes of simulation data, it took some time before researchers could fully understand the implications of their model runs. However, what they saw both elated and surprised them. The stellar gas performed in a manner very much like ordinary convection, with the neutrinos driving the heating process. And that’s not all… They also found strong sloshing motions which transiently change to rotational motions. This behavior has been observed before and named Standing Accretion Shock Instability. According to the news release, “This term expresses the fact that the initial sphericity of the supernova shock wave is spontaneously broken, because the shock develops large-amplitude, pulsating asymmetries by the oscillatory growth of initially small, random seed perturbations. So far, however, this had been found only in simplified and incomplete model simulations.”
“My colleague Thierry Foglizzo at the Service d’ Astrophysique des CEA-Saclay near Paris has obtained a detailed understanding of the growth conditions of this instability”, explains Hans-Thomas Janka, the head of the research team. “He has constructed an experiment, in which a hydraulic jump in a circular water flow exhibits pulsational asymmetries in close analogy to the shock front in the collapsing matter of the supernova core.” Known as Shallow Water Analogue of Shock Instability, the dynamic process can be demonstrated in less technicalized manners by eliminating the important effects of neutrino heating – a reason which causes many astrophysicists to doubt that collapsing stars might go through this type of instability. However, the new computer models are able to demonstrate the Standing Accretion Shock Instability is a critical factor.
“It does not only govern the mass motions in the supernova core but it also imposes characteristic signatures on the neutrino and gravitational-wave emission, which will be measurable for a future Galactic supernova. Moreover, it may lead to strong asymmetries of the stellar explosion, in course of which the newly formed neutron star will receive a large kick and spin”, describes team member Bernhard Müller the most significant consequences of such dynamical processes in the supernova core.
Are we finished with supernova research? Do we understand everything there is to know about neutron stars? Not hardly. At the present time, the scientist are ready to further their investigations into the measurable effects connected to SASI and refine their predictions of associated signals. In the future they will further their understanding by performing more and longer simulations to reveal how instability and neutrino heating react together. Perhaps one day they’ll be able to show this relationship to be the trigger which ignites a supernova explosion and conceives a neutron star.
A sequence of images showing the light echo (circled) enshrouding T Pyxidis months after the April 2011 outburst. (Credit: NASA/ESA/A. Crotts/J. Sokoloski, H. Uthas & S. Lawrence).
Some of the most violent events in our Universe were the topic of discussion this morning at the 222nd meeting of the American Astronomical Society in Indianapolis, Indiana as researchers revealed recent observations of light echoes seen as the result of stellar explosions.
A light echo occurs when we see dust and ejected material illuminated by a brilliant nova. A similar phenomenon results in what is termed as a reflection nebula. A star is said to go nova when a white dwarf star siphons off material from a companion star. This accumulated hydrogen builds up under terrific pressure, sparking a brief outburst of nuclear fusion.
A very special and rare case is a class of cataclysmic variables known as recurrent novae. Less than dozen of these types of stars are known of in our galaxy, and the most famous and bizarre case is that of T Pyxidis.
Located in the southern constellation of Pyxis, T Pyxidis generally hovers around +15th magnitude, a faint target even in a large backyard telescope. It has been prone, however, to great outbursts approaching naked eye brightness roughly every 20 years to magnitude +6.4. That’s a change in brightness almost 4,000-fold.
But the mystery has only deepened surrounding this star. Eight outbursts were monitored by astronomers from 1890 to 1966, and then… nothing. For decades, T Pyxidis was silent. Speculation shifted from when T Pyxidis would pop to why this star was suddenly undergoing a lengthy phase of silence.
Could models for recurrent novae be in need of an overhaul?
T Pyxidis finally answered astronomers’ questions in 2011, undergoing its first outburst in 45 years. And this time, they had the Hubble Space Telescope on hand to witness the event.
Light curve of the 2011 eruption of T Pyxidis. (Credit: AAVSO).
In fact, Hubble had just been refurbished during the final visit of the space shuttle Atlantis to the orbiting observatory in 2009 on STS-125 with the installation of its Wide Field Camera 3, which was used to monitor the outburst of T Pyxidis.
The Hubble observation of the light echo provided some surprises for astronomers as well.
“We fully expected this to be a spherical shell,” Said Columbia University’s Arlin Crotts, referring to the ejecta in the vicinity of the star. “This observation shows it is a disk, and it is populated with fast-moving ejecta from previous outbursts.”
Indeed, this discovery raises some exciting possibilities, such as providing researchers with the ability to map the anatomy of previous outbursts from the star as the light echo evolves and illuminates the 3-D interior of the disk like a Chinese lantern. The disk is inclined about 30 degrees to our line of sight, and researchers suggest that the companion star may play a role in the molding of its structure from a sphere into a disk. The disk of material surrounding T Pyxidis is huge, about 1 light year across. This results in an apparent ring diameter of 6 arc seconds (about 1/8th the apparent size of Jupiter at opposition) as seen from our Earthly vantage point.
Paradoxically, light echoes can appear to move at superluminal speeds. This illusion is a result of the geometry of the path that the light takes to reach the observer, crossing similar distances but arriving at different times.
And speaking of distance, measurement of the light echoes has given astronomers another surprise. T Pyxidis is located about 15,500 light years distant, at the higher 10% end of the previous 6,500-16,000 light year estimated range. This means that T Pyxidis is an intrinsically bright object, and its outbursts are even more energetic than thought.
Light echoes have been studied surrounding other novae, but this has been the first time that scientists have been able to map them extensively in 3 dimensions.
An artist’s conception of the disk of material surrounding T Pyxidis. (Credit: ESA/NASA & A. Feild STScl/AURA).
“We’ve all seen how light from fireworks shells during the grand finale will light up the smoke and soot from the shells earlier in the show,” said team member Stephen Lawrence of Hofstra University. “In an analogous way, we’re using light from T Pyx’s latest outburst and its propagation at the speed of light to dissect its fireworks displays from decades past.”
Researchers also told Universe Today of the role which amateur astronomers have played in monitoring these outbursts. Only so much “scope time” exists, very little of which can be allocated exclusively to the study of light echoes. Amateurs and members of the American Association of Variable Star Observers (AAVSO) are often the first to alert the pros that an outburst is underway. A famous example of this occurred in 2010, when Florida-based backyard observer Barbara Harris was the first to spot an outburst from recurrent novae U Scorpii.
And although T Pyxidis may now be dormant for the next few decades, there are several other recurrent novae worth continued scrutiny:
Name
Max brightness
Right Ascension
Declination
Last Eruption
Period(years)
U Scorpii
+7.5
16H 22’ 31”
-17° 52’ 43”
2010
10
T Pyxidis
+6.4
9H 04’ 42”
-32° 22’ 48”
2011
20
RS Ophiuchi
+4.8
17H 50’ 13”
-6° 42’ 28”
2006
10-20
T Coronae Borealis
+2.5
15H 59’ 30”
25° 55’ 13”
1946
80?
WZ Sagittae
+7.0
20H 07’ 37”
+17° 42’ 15”
2001
30
Clearly, recurrent novae have a tale to tell us of the role they play in the cosmos. Congrats to Lawrence and team on the discovery… keep an eye out from future fireworks from this rare class of star!
An artist's conception of a hypervelocity star that has escaped the Milky Way. Credit: NASA
The Sun is racing through the Galaxy at a speed that is 30 times greater than a space shuttle in orbit (clocking in at 220 km/s with respect to the galactic center). Most stars within the Milky Way travel at a relatively similar speed. But certain stars are definitely breaking the stellar speed limit. About one in a billion stars travel at a speed roughly 3 times greater than our Sun – so fast that they can easily escape the galaxy entirely!
We have discovered dozens of these so-called hypervelocity stars. But how exactly do these stars reach such high speeds? Astronomers from the University of Leicester may have found the answer.
The first clue comes in observing hypervelocity stars, where we can note their speed and direction. From these two measurements, we can trace these stars backward in order to find their origin. Results show that most hypervelocity stars begin moving quickly in the Galactic Center.
We now have a rough idea of where these stars gain their speed, but not how they reach such high velocities. Astronomers think two processes are likely to kick stars to such great speeds. The first process involves an interaction with the supermassive black hole (Sgr A*) at the center of our Galaxy. When a binary star system wanders too close to Sgr A*, one star is likely to be captured, while the other star is likely to be flung away from the black hole at an alarming rate.
The second process involves a supernova explosion in a binary system. Dr. Kastytis Zubovas, lead author on the paper summarized here, told Universe Today, “Supernova explosions in binary systems disrupt those systems and allow the remaining star to fly away, sometimes with enough velocity to escape the Galaxy.”
There is, however, one caveat. Binary stars in the center of our Galaxy will both be orbiting each other and orbiting Sgr A*. They will have two velocities associated with them. “If the velocity of the star around the binary’s center of mass happens to line up closely with the velocity of the center of mass around the supermassive black hole, the combined velocity may be large enough to escape the Galaxy altogether,” explained Zubovas.
In this case, we can’t sit around and wait to observe a supernova explosion breaking up a binary system. We would have to be very lucky to catch that! Instead, astronomers rely on computer modeling to recreate the physics of such an event. They set up multiple calculations in order to determine the statistical probability that the event will occur, and check if the results match observations.
Astronomers from the University of Leicester did just this. Their model includes multiple input parameters, such as the number of binaries, their initial locations, and their orbital parameters. It then calculates when a star might undergo a supernova explosion, and depending on the position of the two stars at that time, the final velocity of the remaining star.
The probability that a supernova disrupts a binary system is greater than 93%. But does the secondary star then escape from the galactic center? Yes, 4 – 25% of the time. Zubovas described, “Even though this is a very rare occurrence, we may expect several tens of such stars to be created over 100 million years.” The final results suggest that this model ejects stars with rates high enough to match the observed number of hypervelocity stars.
Not only do the number of hypervelocity stars match observations but also their distribution throughout space. “Hypervelocity stars produced by our supernova disruption method are not evenly distributed on the sky,” said Dr. Graham Wynn, a co-author on the paper. “They follow a pattern which retains an imprint of the stellar disk they formed in. Observed hypervelocity stars are seen to follow a pattern much like this.”
In the end, the model was very successful at describing the observed properties of hypervelocity stars. Future research will include a more detailed model that will allow astronomers to understand the ultimate fate of hypervelocity stars, the effect that supernova explosions have on their surroundings, and the galactic center itself.
It’s likely that both scenarios – binary systems interacting with the supermassive black hole and one undergoing a supernova explosion – form hypervelocity stars. Studying both will continue to answer questions about how these speedy stars form.
Animation of SN 2011fe in M101. Credit: Virtual Telescope Project
Supernovae are some of the fascinating objects in the Universe. The Virtual Telescope Project will be hosting a live webcast today UPDATE: the webcast will also be on May 17, 2013 as clouds arrived shortly into the webcast on on the 16th) at 21:00 UTC (5 pm EDT, 2 pm PDT) to explore in real-time — from the comfort of your home or office –the exciting world of supernovae, those incredible, violent exploding stars. All this with the live commentary from a professional astrophysicist, Gianluca Masi.
During “The Exploding Universe: the Realm of Supernovae”, you can join in and surf the Cosmos in space and time, observing dying stars placed millions of light years way and shining as billions of Sun, while living the very final stages of their lives, before becoming a neutron star or a black hole.
Hubble image of SNR 0519, the remains of a Type Ia supernova in the Large Magellanic Cloud
Stars like our Sun can last for a very long time (in human terms, anyway!) somewhere in the neighborhood of 10-12 billion years. Already over 4.6 billion years old, the Sun is entering middle age and will keep on happily fusing hydrogen into helium for quite some time. But eventually even stars come to the end of their lives, and their deaths are some of the most powerful — and beautiful — events in the Universe.
The wispy, glowing red structures above are the remains of a white dwarf in the neighboring Large Magellanic Cloud 150,000 light-years away. Supernova remnant SNR 0519 was created about 600 years ago (by our time) when a star like the Sun, in the final stages of its life, gathered enough material from a companion to reach a critical mass and then explode, casting its outer layers far out into space to create the cosmic rose we see today.
As the hydrogen material from the star plows outwards through interstellar space it becomes ionized, glowing bright red.
SNR 0519 is the result of a Type Ia supernova, which are the result of one white dwarf within a binary pair drawing material onto itself from the other until it undergoes a core-collapse and blows apart violently. The binary pair can be two white dwarfs or a white dwarf and another type of star, such as a red giant, but at least one white dwarf is thought to always be the progenitor.
A recent search into the heart of the remnant found no surviving post-main sequence stars, suggesting that SNR 0519 was created by two white dwarfs rather than a mismatched pair. Both stars were likely destroyed in the explosion, as any non-degenerate partner would have remained.
Composite Spitzer, Hubble, and Chandra image of supernova remnant Cassiopeia A. A new study shows that a supernova as far away as 50 light years could have devastating effects on life on Earth. (NASA/JPL-Caltech/STScI/CXC/SAO)
“The total number of stars in the Universe is larger than all the grains of sand on all the beaches of the planet Earth,” Carl Sagan famously said in his iconic TV series Cosmos. But when two of those grains are made of a silicon-and-oxygen compound called silica, and they were found hiding deep inside ancient meteorites recovered from Antarctica, they very well may be from a star… possibly even the one whose explosive collapse sparked the formation of the Solar System itself.
Researchers from Washington University in St. Louis with support from the McDonnell Center for the Space Sciences have announced the discovery of two microscopic grains of silica in primitive meteorites originating from two different sources. This discovery is surprising because silica — one of the main components of sand on Earth today — is not one of the minerals thought to have formed within the Sun’s early circumstellar disk of material.
Instead, it’s thought that the two silica grains were created by a single supernova that seeded the early solar system with its cast-off material and helped set into motion the eventual formation of the planets.
According to a news release by Washington University, “it’s a bit like learning the secrets of the family that lived in your house in the 1800s by examining dust particles they left behind in cracks in the floorboards.”
A 3.5-cm chondrite meteorite found in Antarctica in Nov. 1998. Dark meteorites show up well against the icy terrain of Antarctica. (Carnegie Mellon University)
Until the 1960s most scientists believed the early Solar System got so hot that presolar material could not have survived. But in 1987 scientists at the University of Chicago discovered miniscule diamonds in a primitive meteorite (ones that had not been heated and reworked). Since then they’ve found grains of more than ten other minerals in primitive meteorites.
The scientists can tell these grains came from ancient stars because they have highly unusual isotopic signatures, and different stars produce different proportions of isotopes.
But the material from which our Solar System was fashioned was mixed and homogenized before the planets formed. So all of the planets and the Sun have the pretty much the same “solar” isotopic composition.
Meteorites, most of which are pieces of asteroids, have the solar composition as well, but trapped deep within the primitive ones are pure samples of stars, and the isotopic compositions of these presolar grains can provide clues to their complex nuclear and convective processes.
The layered structure of a star about to go supernova; different layers contain different elements (Wikimedia)
Some models of stellar evolution predict that silica could condense in the cooler outer atmospheres of stars, but others say silicon would be completely consumed by the formation of magnesium- or iron-rich silicates, leaving none to form silica.
“We didn’t know which model was right and which was not, because the models had so many parameters,” said Pierre Haenecour, a graduate student in Earth and Planetary Sciences at Washington University and the first author on a paper to be published in the May 1 issue of Astrophysical Journal Letters.
Under the guidance of physics professor Dr. Christine Floss, who found some of the first silica grains in a meteorite in 2009, Haenecour investigated slices of a primitive meteorite brought back from Antarctica and located a single grain of silica out of 138 presolar grains. The grain he found was rich in oxygen-18, signifying its source as from a core-collapse supernova.
Finding that along with another oxygen-18-enriched silica grain identified within another meteorite by graduate student Xuchao Zhao, Haenecour and his team set about figuring out how such silica grains could form within the collapsing layers of a dying star. They found they could reproduce the oxygen-18 enrichment of the two grains through the mixing of small amounts of material from a star’s oxygen-rich inner zones and the oxygen-18-rich helium/carbon zone with large amounts of material from the outer hydrogen envelope of the supernova.
In fact, Haenecour said, the mixing that produced the composition of the two grains was so similar, the grains might well have come from the same supernova — possibly the very same one that sparked the collapse of the molecular cloud that formed our Solar System.
“It’s a bit like learning the secrets of the family that lived in your house in the 1800s by examining dust particles they left behind in cracks in the floorboards.”
Ancient meteorites, a few microscopic grains of stellar sand, and a lot of lab work… it’s an example of cosmic forensics at its best!
Ancient iron-loving bacteria may have collected particles from a supernova that exploded about 2.2 million years ago. The Crab Nebula, shown here in this image from NASA's Hubble Space Telescope, is much younger having exploded in 1054. Credit: NASA, ESA, J. Hester and A. Loll (Arizona State University)
Ancient iron-loving bacteria may have scooped up evidence of a nearby supernova explosion 2.2 million years ago, leaving an extraterrestrial iron signature in the fossil record, according to German researchers presenting their findings at a recent meeting of the American Physical Society.
In 2004, German scientists reported finding an isotope of iron in a core sample from the Pacific Ocean that does not form on Earth. The scientists calculated the decay rate of the radioactive isotope iron-60 and determined that the source was from a nearby supernova about 2 million years ago. The blast, they say, was close enough to Earth to seriously damage the ozone layer and may have contributed to a marine extinction at the Pliocene-Pleistocene geologic boundary.
Shawn Bishop, a physicist with the Technical University of Munich in Germany and the primary author of the recent study, wondered if traces of the supernova could be found in the fossil record as well. Some deep sea bacteria soak up iron creating tiny magnetic crystals. These 100-nanometer-wide crystals form long chains inside highly-specialized organelles called magnetosomes which help the bacteria orient themselves to Earth’s magnetic field. Using a core sample from the eastern equatorial Pacific Ocean, Bishop and his team sampled strata spaced about 100,000 years apart. By using a chemical treatment that extracts iron-60 while leaving other iron, the scientists then ran the sample through a mass spectrometer to determine whether iron-60 was present.
And in the layers around 2.2 million years ago, tiny traces of iron-60 appeared.
Although the scientists are not sure which star exploded to rain radioactive iron onto Earth, the scientists refer to a paper from 2002 that points to several supernovae generated in the Scorpius-Centaurus star association. The group of young stars, just 130 parsecs (about 424 light-years) from Earth, has produced 20 supernovae within the past 11 million years.
