Massive Cosmic Ring Found Encircling Distant Galaxy.
Astronomers using NASA's Chandra X-ray telescope have spotted a massive ring encircling a distant galaxy in the cosmos.
The strange structure, discovered from a series of X-ray sources, is present around a galaxy named AM 0644-741. It sits some 300 million light-years away from us and is believed to have formed in the wake of a collision between AM 0644 and another smaller galaxy.
NASA recently (https://www.nasa.gov/centers/marshall/history/cosmic-collision-forges-galactic-one-ring-in-x-rays.html) released a composite shot, created by combining optical and X-ray imagery from Hubble and Chandra, showcasing the ring and the galaxies in question.
According to the space agency, the ring formed as the galaxy at the lower left collided with the one on the right - AM 0644. It was pulled by the gravitational force of the latter, which probably created ripples in gas and formed the expanding ring bustling with rapid star formation.
Out of the newborn baby stars, the most massive ones probably led a short life, spanning on the scale of millions of years. They lost their nuclear fuel with time and exploded as supernovae, where the majority of the stellar material is blown away, leaving black holes 5 to 20 times heavier than the sun or dense neutron stars carrying approximately same mass as the sun.
This indicates the ring is either made from stellar-mass black holes or neutron stars that are accompanied by close companion stars. The dense objects are drawing gas from their stellar counterparts, forming a super-hot spinning disk which acts as a detectable X-ray source for Chandra.
Though the researchers behind the discovery - a team from INAF-Osservatorio Astronomico di Brera, Italy - couldn't confirm the identity of individual sources making up the ring, they believe this could either be a case of all black holes or all neutron stars, or a mix of both.
Having that said, it is also worth noting that the X-ray emissions detected from AM 0644 are hundred to thousand times more intense than those seen from other binary systems hosting a star in orbit around a neutron star or a black hole.
This, as the team predicts, could be an effect of the rapid growth of the black holes or neutron stars, or the geometrical effects arising from the stellar material falling into them. Some X-ray sources in the ring are also from objects in the background or within the galaxy. For instance, a rapidly growing black hole that sits behind the galaxy, more than nine billion light-years away from Earth or the supermassive black hole at its center.
The findings of the work, which also included Chandra observations of six more galaxies, could ultimately help scientists understand the effects of massive galactic collisions in the cosmos.
The study, titled "The X-Ray Luminosity Function of Ultra Luminous X-Ray Sources in Collisional Ring Galaxies," was recently published in (http://iopscience.iop.org/article/10.3847/1538-4357/aacb34/meta) the Astrophysical Journal.