A NASA satellite reveals a mystery that flew away in a flash

Shades of blue and bright green in this image of the Fireworks galaxy (NGC 6946) show the location of extremely bright X-ray sources captured by the NASA NASA's NASA space observatory. Generated by some of the most energetic processes in the universe, these X-ray sources are rare compared to the many visible light sources in the background. A new study, published in the Astrophysical Journal, offers some possible explanations for the surprise appearance of the green spring near the center of the galaxy, which appeared and disappeared in a few weeks.

The main objective of NuSTAR observations was to study the supernova – the explosion of a star much more massive than our Sun – which appears in the form of a blue-green spot bright at the top right. These violent events can briefly produce enough visible light to eclipse entire galaxies composed of billions of stars. They also generate many chemical elements in our universe that are heavier than iron.

The green patch near the bottom of the galaxy was not visible at the first observation of NuSTAR but shone at the beginning of a second sighting 10 days later. NASA's Chandra X-ray observatory later observed that the source – known as the ultraluminous X-ray source, or ULX – had disappeared just as quickly. The object has since been named ULX-4 because it is the fourth ULX identified in this galaxy. No visible light source has been detected with the X-ray source, which most likely excludes the possibility that it is also a supernova.

"Ten days, it's really very short for such a brilliant object to appear," said Hannah Earnshaw, a postdoctoral researcher at Caltech in Pasadena, Calif., And lead author of the new study. "Typically, with NuSTAR, we're seeing more gradual changes over time, and we do not often see a source multiple times in a row, so we've been lucky enough to be able to capture a rapidly changing source." which is very exciting. "

Black hole possible

The new study explores the possibility that light comes from a black hole consuming another object, such as a star. If an object approaches too much of a black hole, gravity can separate it, bringing the debris into an orbit close to the black hole. The material located at the inner edge of this newly formed disc begins to move so rapidly that it heats up to millions of degrees and emits X-rays. (In comparison, the surface of the sun is dying). about 10,000 degrees Fahrenheit or 5,500 degrees Celsius.)

Most ULXs usually have a long life because they are created by a dense object, such as a black hole, that "feeds" on the star for an extended period of time. Short-lived or "transient" X-ray sources such as ULX-4 are much rarer, so a single dramatic event, such as a black hole quickly destroying a small star, might explain the observation.

However, ULX-4 may not be an isolated event and the authors of the paper explored other possible explanations for this object. One possibility: the source of ULX-4 could be a neutron star. Neutron stars are extremely dense objects formed by the explosion of a star that was not massive enough to form a black hole. With about the same mass as our Sun but clustered into an object the size of a large city, neutron stars can, like black holes, attract material and create a fast-moving debris disk. . These can also generate sources of slow-moving ultraluminous X-rays, although X-ray light is produced by processes slightly different from ULXs created by black holes.

Neutron stars generate such powerful magnetic fields that they can create "columns" that channel the material to the surface, generating powerful x-rays. But if the neutron star is spinning especially fast, these magnetic fields can create a barrier, thus preventing materials from reaching the star's surface.

"It would be a bit like trying to jump on a carousel that turns thousands of kilometers to the hour," said Earnshaw.

The barrier effect would prevent the star from being a light source of x-rays, except in cases where the magnetic barrier could wobble briefly, allowing the material to slip and fall on the surface of the X-ray. Neutron star. This could be another possible explanation for the sudden appearance and disappearance of ULX-4. If the same source were to reignite, she could support this hypothesis.

"This result is a step forward in understanding the rarest and most extreme cases in which matter accumulates on black holes or neutron stars," said Earnshaw.