They discover a new class of X-ray sources in the cosmos

Some natural cosmic phenomena produce X-rays. For example, the fall of hot gas onto compact objects such as white dwarfs, neutron stars or black holes. Now, astronomers have detected 29 astronomical objects that emit X-rays in strange patterns.

These astronomical objects reside in the Large Magellanic Cloud and the Small Magellanic Cloud, two satellite galaxies of our own.

These objects showed unexpected behavior during the observations. They emitted X-rays, causing their brightness in that band of the electromagnetic spectrum to be between 10 and 20 times greater than usual for several months. Some of these objects experienced such an episode every few years, while others only did so once during the observation period.

The research was carried out by an international team led by Przemek Mróz, from the Astronomical Observatory of the University of Warsaw in Poland.

The team discovered these objects by analyzing more than 20 years of data collected by the OGLE (Optical Gravitational Lensing Experiment) survey, led by astronomers at the University of Warsaw.

Mróz and his colleagues believe that these 29 objects belong to a new class of transient X-ray sources, which they have called “millinovas”, since their maximum brightness is approximately a thousand times lower than that of classical novae. A nova is a huge explosion suffered by a star without being destroyed.

Millinoves are believed to be binary star systems formed by two objects that orbit each other with a period of a few days. A white dwarf (a “retired” star that has ceased its nuclear activity and has shrunk a lot but still emits a lot of light and heat) orbits closely a star that is experiencing the last stage of its active stellar life, a stage in which which has swelled to become a red giant. The proximity between the two stars allows material to flow from the red giant to the white dwarf.

Artistic recreation of a classic nova. (Illustration: Krzysztof Ulaczyk / Astronomical Observatory, University of Warsaw)

The mechanism by which these X-ray emissions are generated is unknown. According to one hypothesis, the X-rays could be produced when material from the red giant falls on the surface of the white dwarf. In any case, more research will have to be done to clarify the mystery.

The study is titled “Millinovae: a new class of transient supersoft X-ray sources without a classical nova eruption.” And it has been published in the academic journal The Astrophysical Journal Letters. (Fountain: NCYT by Amazings)