Supernovae, the spectacular death rattles of the largest stars, are the astronomical gifts that keep giving.
The stellar explosions can add a temporary new jewel to the night (and sometimes day) sky, and they leave behind spectacular and intricate formations known as remnants. A certain class of supernovae helped astronomers realize that the universe’s expansion is speeding up, leading to the “discovery” of dark energy pervading our cosmos. And now, it seems, supernovae might ultimately be to blame for one of astronomy’s longest running mysteries: the origins of cosmic rays.
Scientists have known about these ridiculously energetic and high-velocity particles for nearly a hundred years. In daily life, cosmic rays may be familiar as the source of extra radiation airline passengers are exposed to. However scientists have been uncertain about where cosmic rays come from. The extreme conditions of temperature and speed that accompany supernovae and their remains made them a natural starting point for guesses. Now two separate Science papers finally provide evidence that cosmic rays do indeed come from supernovae remnants.
This colorful supernova remnant is called W49B, and inside it astronomers think they may have found the Milky Way’s youngest black hole. It’s only 1,000 years old, as seen from Earth, and 26,000 lightyears away.
From a vantage point on NASA’s Chandra X-ray Observatory, astronomers observed and measured the remnant and determined it to be very unique. The supernova explosion of this massive star was not symmetrical like most, and instead of collapsing to form a telltale neutron star at its center, this supernova seems to have a black hole.
The most recently observed stellar explosion in our neighborhood
was Kepler’s supernova, spotted 400 years ago.
Scientists using a telescope atop a Hawaiian volcano have detected a pair of extra-bright supernovae, or star explosions, one of which is the oldest, most-distant supernova ever detected.
That explosion occurred 12 billion years ago, making it a billion years older than the oldest supernova ever seen before. Because they are so bright—about 10 to 100 times brighter than most supernovae—these superluminous supernovae extend the limit on how far scientists can look back in time when they study the stars, whose light takes so long to reach us that what they are showing us is a picture of the universe in the past. With these results, published in Nature, scientists are peering closer than ever before to the time of the Big Bang, 13.7 billion years ago. Read More
A page from the Anglo-Saxon Chronicle. The entry for
774 AD refers to a “red crucifix” appearing in the sky.
Earlier this month, researchers found that Japanese trees had preserved a centuries-old spike in the atmosphere’s proportion of carbon-14, apparently caused by a burst of cosmic rays that hit earth between 774 and 775 AD. But that left a perplexing mystery: the most likely source of that excess carbon-14 would be cosmic rays emitted by a supernova. But any supernova powerful enough to generate carbon-14 should have been visible to people alive then, and there was no known record of what should’ve been a pretty notable event.
Enter Jonathon Allen, a polymath undergraduate who majors in biochemistry and also has a deep interest in history. Allen dug around in a contemporary manuscript and found a reference to a “red crucifix” appearing in the sky in 774 AD. This celestial signal may have marked a supernova that birthed the cosmic rays and created the trees’ carbon-14 peak.
A tree’s rings mark both its age and the local environmental conditions, which allows researchers to track historical changes in an ecosystem. But tree rings can also encode signals from beyond Earth: Ancient trees in the Northern Hemisphere have preserved a radioactive souvenir from a 1200-year-old burst of cosmic rays.
Using tree rings, researchers have collected 3,000 years worth of data on the presence of the radioactive carbon isotope carbon-14 in the atmosphere. When examining the ebb and flow of carbon-14 over time, Japanese researchers noticed an increase during the 8th and 9th centuries CE. They decided to look at that period in detail by studying the yearly concentrations of carbon-14 in Japanese cedar trees. The cedars revealed a 1.2 percent carbon-14 spike that lasted less than a year between 774 and 775 CE, which corresponded with similar spikes in North American and European trees. This peak, twenty times the amount of variation normally caused by the sun’s fluctuations, resulted from a short-term burst of cosmic rays. But where did those rays come from—a supernova, a solar flare, or some other source?
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.”
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]
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.
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.
80beats: Detoured Light From Tycho’s Supernova Finally Makes it to Earth
80beats: Mysterious Stellar Blast in the 1840s Was a “Supernova Imposter”
DISCOVER: Sliced: Inside a Supernova
DISCOVER: One Spectacular Stellar Death
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].