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article imageNASA finds youngest black hole in Milky Way, 1000 yrs old

By JohnThomas Didymus     Feb 14, 2013 in Science
NASA scientists believe they may have found the youngest black hole in the Milky Way galaxy formed only about 1,000 years ago, and it is not very far away from Earth, only about 26,000 light-years away.
NASA's Chandra X-Ray Observatory collected data that shows that a black hole may have been formed only very recently, 26,000 light years away.
Laura Lopez, NASA's Einstein fellow and Pappalardo Fellow in Physics at the Massachusetts Institute of Technology, said: "It appears its parent star ended its life in a way that most others don’t."
Theory
The researchers observed a supernova remnant in our Galaxy called W49B which some scientists had argued may have been formed by a gamma-ray burst (GRB). GRBs are extreme supernova explosions believed to be the most energetic and luminous events in the Universe that mark the end of the lives of some very massive stars (more than 25 times the mass of the Sun) after they have exhausted their nuclear fuel. With the star's nuclear fuel exhausted, the energy of reactions that support the star in the core is depleted and it collapses to form a black hole while the outer layers are flung into space in a violent explosion known as a supernova explosion.
Usually, when a supernova explosion forms a black hole, the core material in pulled in entirely. But if it rotates rapidly as it collapses some of the heavier metals in the core may be expelled in jets at the poles of the star at velocities near the speed of light. If these jets are expelled in the direction of the Earth, the energy is beamed in a powerful flash of light called a gamma-ray burst.
With the claim that W49B was formed by a gamma-ray burst in mind, the scientists asked themselves: "What would a gamma-ray burst look like after a thousand years, and what would it leave behind?"
They determined that 1,000 later, the remnant of a gamma-ray burst would look unlike an ordinary supernova. A typical supernova is relativity spherical (see image of E0102 below), but a supernova involving a gamma-ray burst could be expected to have heavy metal jets which after a 1,000 years would have expanded to form a "bar" with a large concentration of iron (see image of W49B below). Because ordinary supernovae formed from core-collapse do not have as much iron as those formed from gamma-ray bursts, scientists can determine a supernova formed from a gamma-ray burst by measuring the amounts of heavy metals such as iron, chromium, and manganese compared with other elements in the supernova.
Supernova E0102
Supernova E0102
NASA
W49B
W49B
NASA
Observing W49B with the Chandra X-ray Observatory
Using the Chandra X-ray Observatory Advanced CCD Imaging Spectrometer (ACIS), the researchers mapped and compared the amount of metals produced in the W49B supernova explosion. According to the researchers, the metals emit plenty of X-rays because they are very hot, allowing the Chandra Observatory images to capture the "bar" of iron in W49B. The observatory also revealed that W49B has relatively low amounts of silicon and sulfur much less than is predicted for typical core-collapse supernova that form spherical cores such as E0102 shown above.
They concluded from the Chandra X-Ray Observatory data that the shape and metals of W49B show the explosion has jets that theory predicts for gamma-ray bursts.
They also used Chandra to search for the compact leftover from the supernova. Theory predicts a gamma-ray burst supernova explosion of a star with mass between eight and twenty times the mass of the Sun should form a neutron star while a gamma-ray burst explosion of much more massive star should form a black hole. Neutron stars are very small stellar leftover of supernova explosion with a radius of only 10 km. Theory predicts that a neutron star should produce a lot of X-rays after a thousand years when the star surface is very hot. With this theoretical background in mind, the researchers, using Chandra, looked for evidence of a neutron star and could not find one.
The Los Angeles Times reports that according to Megan Watzke, press officer at NASA’s Chandra X-Ray Observatory, "it’s that lack of evidence that points to the existence of a black hole."
Watzke said: "In this case... the lack of pulsations.. add to the evidence that a black hole is there. In other situations, however, astronomers can detect the black hole’s presence by its influence on the material around it."
Lopez concluded: "In fact, the deep observation allowed us to say there's no neutron star in W49B that's even 1/100 as bright as astronomers think it would be. This result supports the fact that W49B’s supernova formed a black hole, which is consistent with the explosion having been a gamma-ray burst."
Now, remember that a gamma ray burst is defined with reference to the condition that the jets of heavy metal expelled from the collapsing core are in the direction of the Earth. The researchers explained that with this criterion in mind, W49B probably did not result in a gamma-ray burst from our perspective since the jets were not pointed toward Earth. However, the evidence from the "bar" of iron suggests that the explosion happened perpendicular to our view from Earth and could have been a gamma-ray burst had it been directed or oriented toward the Earth.
The study concluded: "This result means that these exotic explosions can happen within our own Galaxy, and further study of W49B will give great insights into how these awesome events come about."
VOA reports the findings of the study will be published in an upcoming issue of the Astrophysical Journal.
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