Integral gamma-ray observatory demonstrates white dwarfs can reignite and explode as supernovae
(Phys.org) —Astronomers using ESA’s Integral gamma-ray observatory have demonstrated beyond doubt that dead stars known as white dwarfs can reignite and explode as supernovae. The finding came after the unique signature of gamma rays from the radioactive elements created in one of these explosions was captured for the first time.
The explosions in question are known as Type Ia supernovae, long suspected to be the result of a white dwarf star blowing up because of a disruptive interaction with a companion star. However, astronomers have lacked definitive evidence that a white dwarf was involved until now. The ‘smoking gun’ in this case was evidence for radioactive nuclei being created by fusion during the thermonuclear explosion of the white dwarf star.
"Integral has all the capabilities to detect the signature of this fusion, but we had to wait for more than ten years for a once-in-a-lifetime opportunity to catch a nearby supernova," says Eugene Churazov, from the Space Research Institute (IKI) in Moscow, Russia and the Max Planck Institute for Astrophysics,in Garching, Germany.
Although Type Ia supernovae are expected to occur frequently across the Universe they are rare occurrences in any one galaxy, with typical rates of one every few hundred years.
Integral’s chance came on 21 January 2014, when students at the University College London’s teaching observatory at Mill Hill, UK, detected a type Ia supernova, later named SN2014J, in the nearby galaxy M82.
According to the theory of such explosions, the carbon and oxygen found in a white dwarf should be fused into radioactive nickel during the explosion. This nickel should then quickly decay into radioactive cobalt, which would itself subsequently decay, on a somewhat longer timescale, into stable iron.
Because of its proximity – at a distance of about 11.5 million light-years from Earth, SN2014J is the closest of its type to be detected in decades – Integral stood a good chance of seeing the gamma rays produced by the decay. Within one week of the initial discovery, an observing plan to use Integral had been drawn-up and approved.
In January 2014, a supernova was discovered in the nearby galaxy M82. At a distance of about 11.5 million light-years from Earth, SN2014J as it is known, is the closest of its type to be detected in decades. This composite Hubble image shows …more
Using Integral to study the aftermath of the supernova explosion, scientists looked for the signature of cobalt decay – and they found it, in exactly the quantities that the models predicted.
"The consistency of the spectra, obtained by Integral 50 days after the explosion, with that expected from cobalt decay in the expanding debris of the white dwarf was excellent," says Churazov, who is lead author of a paper describing this study and reported in the journal Nature.
With that confirmation in hand, other astronomers could begin to look into the details of the process. In particular, how the white dwarf is detonated in the first place.
White dwarfs are inert stars that contain up to 1.4 times the mass of the Sun squeezed into a volume about the same size as the Earth. Being inert, they can’t simply blow themselves up. Instead, astronomers believe that they leech matter from a companion star, which builds up on the surface until a critical total mass is reached. At that point, the pressure in the heart of the white dwarf triggers a catastrophic thermonuclear detonation.
Early Integral observations of SN2014J tell a somewhat different story, and have been the focus of a separate study, reported online in Science Express by Roland Diehl from the Max Planck Institute for Extraterrestrial Physics, Germany, and colleagues.
Diehl and his colleagues detected gamma rays from the decay of radioactive nickel just 15 days after the explosion. This was unexpected, because during the early phase of a Type Ia supernova, the explosion debris is thought to be so dense that the gamma rays from the nickel decay should be trapped inside.
"We were puzzled by this surprising signal, and some from the group even thought it must be wrong," says Diehl. "We had long and ultimately very fruitful discussions about what might explain these data."
A careful examination of the theory showed that the signal would have been hidden only if the explosion had begun in the heart of the white dwarf. Instead, Diehl and colleagues think that what they are seeing is evidence for a belt of gas from the companion star that must have built up around the equator of the white dwarf. This outer layer detonated, forming the observed nickel and then triggering the internal explosion that became the supernova.
"Regardless of the fine details of how these supernovae are triggered, Integral has proved beyond doubt that a white dwarf is involved in these stellar cataclysms," says Erik Kuulkers, ESA’s Integral Project Scientist. "This clearly demonstrates that even after almost twelve years in operation, Integral is still playing a crucial role in unraveling some of the mysteries of the high-energy Universe."
The evolutionary tree for modern humans a bit of a mess - humans haven’t had a close relative on this planet for over 10,000 years, but there used to be several other closely related species living at the same time. Genetic analyses on bone fragments from Neanderthals and Denisovans has given us new insight into our not-so-distant evolutionary past. The results indicate that not only did Denisovans and Neanderthals interbreed with modern Homo sapiens, but they also mated with an unidentified fourth hominin group. This information was presented to evolutionary geneticists last week for a meeting of the Royal Society.
Neanderthals emerged about 200,000 years ago and remains have been found throughout Europe, stretching into central Asia. While Neanderthals weren’t as cognitively advanced as Homo sapiens who emerged around the same time, they were probably the first hominins known to wear clothing, bury dead, and form languages. It has been traditionally thought that the last common ancestor of Homo sapiens and Neanderthals existed around 400,000 years ago, though new research suggests it could have been earlier.
Denisovans are an extinct group of hominins that are part of our evolutionary lineage. Our knowledge of them comes from bone fragments found in a cave that date back about 30,000-50,000 years. Though genetic analysis had been done a couple years ago, the results weren’t really clear. New techniques have yielded much more complete genetic sequences and two new studies have released different yet related results.
There is evidence of certain populations of humans alive today getting as much as 4% of their DNA from Denisovans, though there is some debate surrounding it. Additionally, there are people with ancestries outside of Africa that could have gotten about 2% of their genomes from Neanderthals, though there is some speculation with this as well.
Right now, the identity of this fourth early human group remains a mystery. They could have come from Asia, but that has not yet been made certain. Future research will hopefully identify this unknown population and help us better understand all of the different evolutionary inputs that make us who we are.
BROTHER AND SISTER FACE INCEST CHARGES, BLAME 'THE NOTEBOOK'
BRB, dying laughing and puking at the same time…
GUYTON, Ga. —Police arrested a brother and sister after they say the two admitted to having sex in a tractor trailer sitting in a church parking lot.
Police had been called to a Baptist church in Guyton, Georgia, on reports of a prowler, ABC affiliate WJCL-TV reports. When officers arrived, they found a man and woman walking down the street near the church.
At first, Timothy Savoy, 25, told them he was walking Christopher Buckner, 20, back to her house. Minutes later, the pair admitted they were brother and sister and had just finished having sex three times in a Kenworth tractor trailer parked outside the church.
The brother and sister blamed their behavior on the fact that they had just finished watching “The Notebook.” Both are charged with aggravated sodomy, incest and prowling.
Try not be too jealous, but I apparently kept my new friend in China so busy with all these orders from tumblr, that I was told that I get a space bedding set for free, shipping included. I was so excited that I actually called my Mom. Nice to know that at almost 29, I can still be elated over a space bedding set. I’m more elated at the fact that I have so many badass space people following me that a post like that could gain such popularity that it translated to actual sales for someone. The post is now at 50,000 notes! Maybe I should do this more often….
Our sense of scale tends to adjust to circumstances. So when we think about comets it is easy to compare them with other astronomical objects. In which case comet 67P/Churyumov-Gerasimenko, just 3km wide, sounds tiny.
However, as you can see in the image above, things look rather different when you compare the comet to something we are really familiar with - such as tall buildings.
While Churyumov-Gerasimenko is small enough that one could walk from one end to the other fairly in less than an hour, it’s easy to forget the three dimensional nature of something like this – 3km across is no big deal, but two kilometers helps make sense of what happened to the dinosaurs.
The image is by @quark1972, who combined a photogrph of Los Angeles with an image from the Rosetta spacecraft rendezvousing with Churyumov-Gerasimenko, prior to going into orbit and eventually landing.
While Rosetta will be doing its best to touch down very gently on the comet’s surface, we can’t count on Churyumov-Gerasimenko doing the same if it ever paid LA a visit. You can get some idea of what would happen in such a collision here, although the scale of the damage depends greatly on the impact speed you choose to enter.
Since Churyumov-Gerasimenko never crosses the Earth’s orbit there is no danger of a collision, at least until a close encounter with some other planet shifts its orbit. Unfortunately the same cannot be said for other, even larger, asteroids and comets.