What’s the News: Astronomers have known for a while that white dwarfs can sometimes ignite in massive explosions known as Type Ia supernovae, but they haven’t been sure what pulls the trigger. One theory says that the explosion occurs when two white dwarfs merge into each other, while an opposing theory says that it happens when a single white dwarf pulls material from a Sun-like companion star. Using the Chandra X-ray telescope, astronomers have discovered an arc-shaped material emitting X-rays in the Tycho supernova that gives hints about the supernova’s origin. “This stripped stellar material was the missing piece of the puzzle for arguing that Tycho’s supernova was triggered in a binary with a normal stellar companion,” says Fangjun Lu. “We now seem to have found this piece.”
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Where once there was a star 20 times the size of our sun, now there is a record breaker. Astronomers report this week in Nature that when the huge star went supernova, it collapsed into a neutron star that is heaviest they’ve ever seen, with twice the mass of our sun compacted into a tiny space. Aside from taking its place in the record books, this massive monster could reveal what truly goes on deep in the heart of a deceased star.
The neutron star is part of a binary star system called J1614-2230, in which it and a white dwarf are locked in a spin cycle. Thanks to the neutron star’s steady emission of radio waves and a handy trick of relativity, scientists can measure the size of the two objects despite the fact that they’re 3,000 light years from here.
The astronomers took detailed measurements of the radio pulses that reached Earth. As these pulses, which originate from the rotation of the neutron star, passed by the companion white dwarf, their timing was delayed due to the highly warped nature of spacetime—an effect known as Shapiro delay. In a highly inclined, nearly edge-on system such as J1614-2230 the effect allows astronomers to make very accurate measurements both of the neutron star and its companion. [Ars Technica]
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The one ring is back, and it’s beautiful.
What you see here is the aftermath of stellar death, rediscovered after NASA temporarily lost the ability to watch it play out. Astronomers tracked supernova 1987A after its discovery that year, picking up insights into what happens after a huge star expends itself. But in 2004, the Hubble Space Telescope‘s Space Telescope Imaging Spectrograph went kaput. The May 2009 space shuttle servicing mission repaired this eye in the sky, leading to a study in this week’s edition of the journal Science that reveals what’s behind this fluorescent view, and why that ring shines so brightly.
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A supernova that was observed in 1680 by Britain’s first Astronomer Royal, John Flamsteed, has been revealed to have produced a strange little neutron star that will give astronomers insight into how such stars are born and mature. The remains of the supernova, known as Cassiopeia A, have been something of a mystery to astronomers. Supernovae usually leave behind an extremely dense object such as a black hole or neutron star. But for decades no such object was seen at the centre of Cassiopeia A [Nature News]. Now new observations suggest that the 330-year-old neutron star escaped detection because of its odd atmosphere.
Instead of resembling more mature neutron stars, which are surrounded by hydrogen, this baby star is blanketed in carbon gas – a discovery that could provide important new insights into the evolution of neutron stars [Physics World]. The new study, published in Nature, suggests that the star is still extremely hot in the aftermath of the supernova–about 2 billion degrees Fahrenheit. This overheated condition caused a nuclear fusion reaction on the star’s surface that converts all the hydrogen and helium into carbon gas, researchers say. As time goes on, and as the star cools, the researchers think the surface fusion reaction will stop and the star will develop a more traditional hydrogen atmosphere.
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Image: NASA / CXC / Southampton / W. Ho / M. Weiss
Physicists in Washington State and Louisiana recently spent two years hunting for the mysterious gravitational waves first predicted by Einstein, but detected nothing: zilch, zero, nada, nary a ripple. But that “null result” is itself of great value, researchers say, because it tells them where to look for the waves next. The findings are a nice reminder that scientific progress isn’t always about the dramatic discovery; it’s often a long, careful process of testing hypotheses, analyzing results, and heading back to the drawing board.
Einstein’s theory of general relativity states that every time mass accelerates — even when you rise up out of your chair — the curvature of space-time changes, and ripples are produced. However, the gravitational waves produced by one person are so small as to be negligible. The waves produced by large masses, though, such as the collision of two black holes or a large supernova explosion, could be large enough to be detected [SPACE.com].
Beyond those large disturbances, the universe is thought to be filled with small disturbances left over from the rapid period of expansion that followed the Big Bang, in a phenomenon known as the stochastic (meaning randomly distributed) gravitational wave background. If the expansion of the newborn universe had produced strong gravity waves, the physicists working at the two Laser Interferometer Gravitational-wave Observatory (LIGO) centers would have detected them. Since they found nothing, researchers have determined that smaller waves were produced, which they’ll need more sensitive instruments to detect. Says study coauthor Vuk Mandic: “We now know a bit more about parameters that describe the evolution of the universe when it was less than one minute old” [Sky & Telescope].
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Astronomers have caught sight of two stars that went kaboom only 2.5 billion years after our universe was created in the Big Bang, and say that ancient explosions are the oldest and most distant supernovas ever discovered. Researchers plan to use the new technique used to identify these supernovas to find other stars that blew up in the universe’s early days, which may aid our understanding of how the universe was seeded with heavy elements.
Only a few lightweight elements – hydrogen, helium, and lithium – are thought to have been created in the big bang; all others were forged over time in the nuclear furnaces of stars and in supernovae. Since the spectrum of light from a supernova reveals the chemical composition of the exploding star, observing many such explosions would allow astronomers to trace out a chemical history of the universe [New Scientist]. Heavier metals eventually gathered in the clouds of dust that surrounded young stars, and sometimes formed parts of rocky planets like Earth.
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A supernova first observed in the 16th century by Danish astronomer Tycho Brahe has been sighted again, astronomers report. Brahe observed its direct light but “light echoes” from the supernova that took a long detour around the universe have finally made it to Earth and have been captured by the Subaru Telescope in Hawaii. The new observations confirm that the supernova was the explosion of a white dwarf star. “Using light echoes in supernova remnants is time-traveling in a way, in that it allows us to go back hundreds of years to observe the first light from a supernova event,” said Tomonori Usuda, lead project astronomer at Subaru [Space.com].
In November 1572, Brahe noted a new shimmer in the night sky and thought it was the birth of a new star. But the shimmer disappeared 16 months later and some claimed it was a comet. Only in the early 20th century did astronomers understand that the fleeting brightness was a supernova and represented not the birth but the death throes of a star. The direct light from the supernova swept past Earth long ago. But some of it struck dust clouds in deep space, causing them to brighten [AP]. These light echoes are what astronomers have now captured and reported in Nature [subscription required]. “What we have essentially done here is to use interstellar dust as a kind of a mirror,” says [co-author] Oliver Krause [Nature News].
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The Fermi Gamma-ray Space Telescope only settled into its orbit a few months ago, but it’s already producing results that are delighting astronomers. Yesterday, NASA announced that Fermi had found a strange pulsar (a fast-spinning neutron star) by detecting only the gamma rays it emits. This is a first, NASA explains. Although astronomers have catalogued nearly 1800 pulsars, this is the first pulsar that seems to emit only gamma-ray radiation. Most other pulsars have been found using radio telescopes, although some also beam energy in visible light and X-rays [New Scientist].
Neutron stars are the small and incredibly dense bodies formed when massive stars explode into supernovas; perhaps the oddest of neutron stars are pulsars, which send out jets of radiation from their magnetic poles that sweep across Earth’s line of sight as the star spins on its axis. The newfound pulsar, which sits 4,600 light-years away in the constellation Cepheus, rotates at about a million miles an hour, and its beam of gamma rays reaches Earth about three times a second [National Geographic News]. Pulsars are often compared to lighthouses for the way their beams flash across our telescopes (see NASA animation).
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A remarkable stellar event that mesmerized astronomers in 1843 may have been a previously unknown kind of explosion, researchers say. That explosion, which made the star Eta Carinae one of the brightest in the Southern sky, could have been the precursor to the star’s expected explosion into a supernova.
Researchers began watching Eta Carinae after the star mysteriously brightened 1843, and astronomers in recent decades have photographed and studied the resulting cloud of gas and dust, known as the Homunculus Nebula, that billows away from the star. A farther-out faint shell of debris from an earlier explosion is also visible, probably dating from around 1,000 years ago. “Looking at other galaxies, astronomers have seen stars like Eta Carinae that get brighter, but not quite as bright as a real supernova,” said [lead researcher] Nathan Smith…. “We don’t know what they are. It’s an enduring mystery as to what can brighten a star that much without destroying it completely” [SPACE.com].
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For million of years after the Big Bang, the universe was a dark place filled only with wisps of hydrogen and helium, as well as the mysterious substance known as dark matter that makes up much of the universe’s mass. Now, researchers have finished running a sophisticated computer program that simulated those early cosmic conditions and replicated the production of the first primordial star, which cast the first rays of starlight out into the blackness. Researchers say that the new model shows that the first star was tiny, but rapidly grew to enormous proportions before either flaming out or collapsing.
In the early universe, researchers believe that clouds of dark matter gathered and compressed pockets of hydrogen and helium gases. According the researchers’ simulation, those areas reached a tipping point around 300 million years after the Big Bang, igniting the first nuclear reactions. Over the course of about 100,000 years, according to the model, the compressed gases reach densities roughly equivalent to that of liquid water on Earth. At that point, the gases inside the halo have formed a protostar, about one-hundredth the mass of the sun [Science News].
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Astronomers have discovered that a massive star known as the Peony Nebula star ranks as the second-brightest in our Milky Way galaxy. The astronomers estimate that the star shines 3.2 million times as brightly as our sun, which is enough to get it a galactic silver medal; the brightest star ever detected is Eta Carinae, which is 4.7 million times brighter than our own little star.
The Peony nebula star… doesn’t look all that bright to the naked eye. Sirius is still the undisputed local champion, based on what we can see in the night sky. But a big factor behind Sirius’ apparent brightness is its relative proximity to Earth – a mere 8.7 light-years, or roughly 50 trillion miles [MSNBC]. In contrast, the Peony Nebula star lies about 26,000 light-years away, in the dusty heart of the Milky Way. In their upcoming report in the journal Astronomy & Astrophysics, researchers say the Spitzer telescope could reveal many other super-bright stars in the same region.
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