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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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