What makes a dead star glow brighter decades after death?
After the explosion of a massive star, the X-ray glow usually gradually weakens. The hot gas is expanding, the shock wave goes further from the explosion site, and the remnant of the supernova slowly loses its brightness. But the data of the NASA Chandra X-ray Observatory showed that in the galaxy M83 everything is not so calm: part of the old stellar explosions for 14 years markedly changing the brightness, although astronomers were waiting for a smoother attenuation.
The researchers studied Chandra observations from 2000 to 2014. The sample includes the remains of supernovae in the galaxy Messier 83, or M83, which is about 15 million light-years from Earth. This spiral galaxy is also known as the Southern Turner. It is actively born new stars, and the most massive of them quickly pass through the life cycle and end with its explosion.
The work showed that in a number of supernovae, X-ray radiation was not just weakened. Some sources became brighter, others were faded, and the overall picture was noticeably more diverse than the standard expectations for the aging shells after the explosion.
The remains of a supernova is not the star itself, but everything that remains after the disaster: hot gas, ejected matter, shock waves and sometimes a compact object in the center. If the core of the deceased star has not collapsed completely, a neutron star or black hole may remain after the explosion. In the X-ray range, such systems glow, because the gas is heated to very high temperatures.
For individual X-ray sources, the variable brightness does not look like something new. Neutron stars, black holes and binary systems can dramatically alter radiation when matter falls on a compact object unevenly. In the case of M83, it was surprising: similar behavior was found immediately in a group of objects that were considered supernova residues. That is, it is not about a single flash, but about a set of sources with unexpected dynamics.
One example is set out against the rest. The balance of the SN 1957D is associated with a supernova, which was first noticed almost 70 years ago. In this case, the substance after the explosion, apparently, collides with the surrounding material. Such material could be discarded by a star even before death or be near in an interstellar environment. The collision heats the gas and enhances X-rays, so the brightness of the source grows.
With other objects, everything is more complicated. One version is associated with surviving companion stars. Many massive stars are born and live in a pair. If a heavier star explodes first, the neighboring one may survive. After the explosion, a neutron star or black hole remains nearby, and the second star continues to revolve around it.
In such a system, a compact object can pull the gas from the companion star. The gas accelerates, heats up and begins to emit in the X-ray range. Such objects are called massive X-ray binary systems, or HMXB. They have long been known to astronomers, but they were not associated with a large number of supernova remnants before. M83 observations show that communication can occur more frequently than thought.
There is another possible cause of variability. After the explosion, part of the ejected substance may not fly completely, and later return to a compact object in the center. If the gas falls on a neutron star or a black hole, it heats up again and gives X-rays. In such a scheme, the material, thrown out by a supernova, after a while begins to fuel the object that remained after the explosion.
These explanations can work in parallel. In one source, the brightness may change due to a collision of the shell with the surrounding gas, the other - because of the companion star, the third - due to the fall of the substance on a neutron star or a black hole. Therefore, researchers do not reduce the entire sample to one mechanism.
It is not too far away to M83. 15 million light-years by cosmic standards, but there is still a lot to study in detail the individual remnants of supernova. Chandra allows you to see X-ray sources and track their brightness by the years, but does not always give enough details to immediately separate the hot shell, a compact object and a possible dual system.
Interest in the discovery intensified after another galaxy was checked. Similar variable remnants of supernovae were found in Messier 51, a whirlpool galaxy. So, the M83 may not be an exception, but the first well-studied example of a more common phenomenon. Further observations should show how many old supernovae continue to change X-rays decades after the explosion.
After the explosion of a massive star, the X-ray glow usually gradually weakens. The hot gas is expanding, the shock wave goes further from the explosion site, and the remnant of the supernova slowly loses its brightness. But the data of the NASA Chandra X-ray Observatory showed that in the galaxy M83 everything is not so calm: part of the old stellar explosions for 14 years markedly changing the brightness, although astronomers were waiting for a smoother attenuation.
The researchers studied Chandra observations from 2000 to 2014. The sample includes the remains of supernovae in the galaxy Messier 83, or M83, which is about 15 million light-years from Earth. This spiral galaxy is also known as the Southern Turner. It is actively born new stars, and the most massive of them quickly pass through the life cycle and end with its explosion.
The work showed that in a number of supernovae, X-ray radiation was not just weakened. Some sources became brighter, others were faded, and the overall picture was noticeably more diverse than the standard expectations for the aging shells after the explosion.
The remains of a supernova is not the star itself, but everything that remains after the disaster: hot gas, ejected matter, shock waves and sometimes a compact object in the center. If the core of the deceased star has not collapsed completely, a neutron star or black hole may remain after the explosion. In the X-ray range, such systems glow, because the gas is heated to very high temperatures.
For individual X-ray sources, the variable brightness does not look like something new. Neutron stars, black holes and binary systems can dramatically alter radiation when matter falls on a compact object unevenly. In the case of M83, it was surprising: similar behavior was found immediately in a group of objects that were considered supernova residues. That is, it is not about a single flash, but about a set of sources with unexpected dynamics.
One example is set out against the rest. The balance of the SN 1957D is associated with a supernova, which was first noticed almost 70 years ago. In this case, the substance after the explosion, apparently, collides with the surrounding material. Such material could be discarded by a star even before death or be near in an interstellar environment. The collision heats the gas and enhances X-rays, so the brightness of the source grows.
With other objects, everything is more complicated. One version is associated with surviving companion stars. Many massive stars are born and live in a pair. If a heavier star explodes first, the neighboring one may survive. After the explosion, a neutron star or black hole remains nearby, and the second star continues to revolve around it.
In such a system, a compact object can pull the gas from the companion star. The gas accelerates, heats up and begins to emit in the X-ray range. Such objects are called massive X-ray binary systems, or HMXB. They have long been known to astronomers, but they were not associated with a large number of supernova remnants before. M83 observations show that communication can occur more frequently than thought.
There is another possible cause of variability. After the explosion, part of the ejected substance may not fly completely, and later return to a compact object in the center. If the gas falls on a neutron star or a black hole, it heats up again and gives X-rays. In such a scheme, the material, thrown out by a supernova, after a while begins to fuel the object that remained after the explosion.
These explanations can work in parallel. In one source, the brightness may change due to a collision of the shell with the surrounding gas, the other - because of the companion star, the third - due to the fall of the substance on a neutron star or a black hole. Therefore, researchers do not reduce the entire sample to one mechanism.
It is not too far away to M83. 15 million light-years by cosmic standards, but there is still a lot to study in detail the individual remnants of supernova. Chandra allows you to see X-ray sources and track their brightness by the years, but does not always give enough details to immediately separate the hot shell, a compact object and a possible dual system.
Interest in the discovery intensified after another galaxy was checked. Similar variable remnants of supernovae were found in Messier 51, a whirlpool galaxy. So, the M83 may not be an exception, but the first well-studied example of a more common phenomenon. Further observations should show how many old supernovae continue to change X-rays decades after the explosion.
