Discovery of a star millions of times brighter than the Sun

Astronomers have found a new member of a rare class of celestial objects called ultraluminous X-ray sources (ULXs) that are millions of times brighter than the Sun in the Whirlpool galaxy about 31 million light-years from Earth,SpaceMarch 1 news.

Experts once thought that ULXs were black holes. However, recent studies have shown that three ULXs are actually super-dense neutron stars. With the new discovery, the total number of observed ULXs is four. The discovery also provides more information to help the research team understand what makes these objects shine so brightly.

In the 1980s, astronomers discovered a number of very bright X-ray sources near the outer edges of galaxies, far from the giant black holes at their centers. By 2014, observations with NASA’s NuSTAR space telescope and other telescopes showed that some of these objects were actually neutron stars, the dense cores left after massive stars collapse.

The new ULX was discovered using NASA’s Chandra X-ray telescope. Scientists initially noticed an unusual dip in the object’s spectrum, which they determined was caused by charged particles swirling around a magnetic field. Since black holes don’t have magnetic fields, this dip pointed to the ULX being a neutron star.

Neutron stars are very dense and massive. A spoonful of material from a neutron star can weigh a billion tons. The intense gravity of a neutron star can pull in material from other stars. This material heats up and emits X-rays as it is pulled into the neutron star. Eventually, these X-rays overcome the star’s gravity and push the material away. In ULX neutron stars, these X-rays are much more intense than normal.

"Just like we can only eat a certain amount of food at a time, there are limits to how fast neutron stars can grow. However, ULXs somehow break this limit to emit super-bright X-rays. We don't know why," said Murray Brightman, lead author of the study and a researcher at the California Institute of Technology.

The team plans to collect more data on ULXs to learn why neutron stars exceed this limit and shine so brightly.