Astronomers have used NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR) to detect the brightest-ever recorded pulsar. The distant object was happened upon by the team while observing a recent supernova in the region. In the long run, the discovery may improve our understanding of how black holes grow.
The object in question, which is located some 12 million light-years away in the Messier 82 (M82) galaxy, is the remnant of a black hole. The pulsar is similar to a black hole in that it’s the burnt-out core resulting from a supernova explosion, but unlike those objects, is only roughly the size of Pasadena. While its mass is about equal to that of our sun, its energy output is some 10 million times as great.
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In the past NuSTAR has been used to provide hints about how stars go supernova, details on star dust formation around them and far more. While the telescope may not have been intentionally looking for the pulsar, known as M82 X-2 (it was actually observing a recent supernova in the region), its findings are helping astronomers to better understand ultra luminous X-rays (ULXs). Black holes do not pulsate as pulsars do, making NuSTAR’s ability to accurately measure the pulse rate of the dead star key to its success in making the discovery.
The Messier 82 (M82) galaxy shown in a visible-light view from NASA's Hubble Space Telescope (left), and an X-ray view from NASA's Chandra X-ray Observatory (right) (Image: NASA/STScI/SAO)
ULXs are intense X-rays that are thought to be produced by long sought-after "medium-size" black holes in the process of engulfing companion stars. NuSTAR’s observations prove that this isn’t always the case, and that ULXs can in fact be produced by pulsars.
Once the team had observed the pulsations in the data, and determined that the ULXs were not emanating from a black hole, it enlisted the help of NASA’s Chandra X-Ray Observatory and Swift satellite to confirm that the source was indeed a pulsar.
At this stage, astronomers aren’t certain why the pulsar’s energy output is so high, but it’s thought likely that the tiny neutron star is pulling in matter from nearby stars. As it absorbs the companion star’s matter, its temperature increases and it emits more and more X-rays. However, this analogy poses more questions than it answers, with theorists unsure how the pulsar can be absorbing surrounding matter at such an extreme rate.
With research into ULXs still in the early stages, it’s unclear whether more pulsars will be discovered emitting the rays, or whether the M82 X-2 is an exception to the rule. Looking forward, it will be up to the NuSTAR, Chandra and Swift telescopes to study both M82 X-2 and other sources of ULXs, with the goal of solving the mystery.
Check out the video below for an animation of the M82 X-2 pulsar.