Cataclysmic stars emit X-rays in a previously unknown way
An international team of scientists, with the participation of astronomers from the Warsaw University Astronomical Observatory, has discovered previously unknown mechanisms of X-ray production in so-called “white dwarfs. cataclysmic stars. The research may also change the way measurements of the expansion rate of the Universe are made.
Astronomers have detected a bright X-ray flare coming from a star located in the Small Magellanic Cloud, a nearby galaxy nearly 200,000 light-years from Earth. A combination of X-ray and optical data indicates that the source of theoThe source of this radiation is a white dwarf, ktory could be the fastest growing white dwarf ever observed.
New analyses based on observational data acquired with the Chandra X-ray Observatory and Swift Observatory have pointed to characteristic X-ray emission from the system subojnego containing a white dwarf named ASASSN-16oh.
Unlike our Sun, most stars, including very dense white dwarfs, do not exist in isolation, but instead are part of pairs. This so-called. sub systemsojne. This is also the case with ASASSN-16oh. It is in fact a system of a white dwarf and a red giant. If the stars are close enough to each other, the white dwarf’s greater gravity can cause matter to flow away from its companion.
Astronomers have detected very bright X-ray emission The discovery includes the emission of so-called “soft X-rays. soft X-rays – radiation at the lowest energies, ktore is produced by gas at temperatures of several hundred thousand degrees. On the other hand, the observed emission of large amounts of radiation must have originated at temperatures on the order of a millionoin degrees. X-ray emission from ASASSN-16oh is much brighter than the soft X-rays produced by the atmospheres of normal stars. Scientists have placed it in a special category of super-soft sourceox-ray sources.
For years, astronomers have thought that supernovae of X-rays from the surface of white dwarfsow is formed by nuclear fusion of material stolen from the companion star’s. When a white dwarf accumulates enough gas and becomes hot enough, thermonuclear reactions start in it and the entire surface of the star explodes. But ASASSN-16oh observations rule out such a violent explosion.
If nuclear fusion were the cause of the super-soft X-rays from ASASSN-16oh, woat the time astronomers should see an explosion, and the emission should come from the entire surface of the white dwarf. However, the light does not grow fast enough to indicate an outburst, and data from the Chandra X-ray Observatory show that the emission comes from a small portion of the white dwarf’s surface.
The discovery of a new mechanism for producing X-rays has been published on the „Nature Astronomy”. An international team of scientistsoin whichory behind the publication, enter roalso astronomers from the Warsaw University Astronomical Observatory.
Observations made by scientists provide a strong argumentow against fusion, ktora could be the source of theoemission drone. The authors of the publication presented another scenario. As with the condition ofow needed for a fusion reaction to occur on a white dwarf, the burned-out star takes gas from a companion star, a red giant. In a process called accretion, gas is pulled into the large disk surrounding the white dwarf and becomes hotter. It then descends on the star, producing X-rays where it meets the star. The rate of matter flow from one star to another is not stable. As the material begins to fall faster, the system’s brightness will increase rapidly.
– In the past, the supermassive sourceodles have been associated with nuclear fusion on the surface of white dwarfsow – said the headowny author of the publication Tom Maccarone, a professor at Texas Tech University. But the new discovery shows that there are two types of soft X-ray production: thermonuclear fusion reactions and accretion.
– Our result contradicts the consensus on how supersoft X-rays are emitted from white dwarfsow – said wsporoutor Thomas Nelson of the University of Pittsburgh. – We now know that X-rays can be produced at two rodifferent ways: by nuclear fusion or by accretion of matter from a companion – added.
But the discoveries may roalso contribute to a better understanding of the expansion of the Universe. In a system like ASASSN-16oh, the white dwarf can continue to gain mass, which will end up in a type Ia supernova. And such events are used to measure just thatoin the expansion of the Universe, because their radiative power is believed to be constant – By measuring the observed brightness of a supernova, one can measure the distance to the parent galaxy.
Type Ia supernovae are presumed to be formed by explosionsoin white dwarfsow, however, the mechanism of the explosions and their origin are not well understood, and it is not known whether supernovae formed in the oldest galaxies look the same as the present ones. Discovery shows that white dwarf-red giant systems, similar to ASASSN-16oh, may become type Ia supernovae in the future.