An unusual explosion shot the star on a journey across the Milky Way

An exploding white dwarf has escaped from its orbit in a binary system during a partial supernova explosion and is now speeding through our galaxy at enormous speed.

This discovery indicates that perhaps there are many more objects in the Milky Way that survived the supernova explosion and travel unnoticed through interstellar space.

The above conclusions are based on the study of a white dwarf, in whose surroundings scientists have previously discovered an unusual atmosphere. Its chemical composition indicates that the star was most likely a constituent of the binary system in which the supernova partially exploded. During this explosion, both components of the system were launched in opposite directions into interstellar space.

What is a white dwarf ?

The white dwarf is actually the nucleus of the red giant remaining after the death of the star and its rejection of its outer layers. It cools down over the next billions of years, gradually losing its brilliance and temperature. Most white dwarfs have atmospheres consisting almost exclusively of hydrogen and helium. From time to time, carbon and oxygen from inside the star are also registered.

White dwarf

Observed by scientists, the SDSS star J1240 + 6710 discovered in 2015 did not contain hydrogen or helium in the atmosphere. Instead, it was surrounded by a layer of oxygen, neon, magnesium and silicon. Using the Hubble Space Telescope, scientists also identified sodium and aluminum carbon in it - all of these elements are formed in the first thermonuclear reactions that occur during a supernova explosion.

When the supernova explosion turns out to be a misfire

However, in the atmosphere of the same white dwarf, elements such as iron, nickel, chromium and manganese are clearly lacking. These heavier elements usually arise from the lighter ones and are a characteristic element of the fusion supernovae. The lack of elements from the iron group in the star SDSS J1240 + 6710 indicates that in her case only a partial supernova occurred.

Measuring the speed of the white dwarf indicates that it is traveling at a speed of 900,000 km / h. As for a white dwarf, it also has a relatively low mass - only 40% of the mass of the Sun, which agrees with the loss of mass during a partial supernova explosion.

Scientists suspect that the supernova disrupted the orbit of the white dwarf and the associated binary star by rapidly rejecting a large part of the mass. At this point, both stars were ejected in opposite directions at their orbital speeds. Such a scenario well explains the high speed of the white dwarf.

If it was a very tight binary system and there was a fusion ignition, rejection of a large amount of mass, then we have ideal conditions for the formation of a white dwarf with low mass and enormous speed - says prof. Boris Gaensicke from the Faculty of Physics at the University of Warwick.

Not all supernovae are the same

The most studied fusion supernovae are Type Ia supernovae, which led to the discovery of dark energy and have long been used to create distance maps in the universe. However, there is growing evidence that thermonuclear supernovae can explode in many different situations.

SDSS J1240 + 6710 may be a supernova remnant of the type we have never seen before. Without the radioactive nickel that supplies long-lasting glow to Type Ia supernovae, the explosion that fired SDSS J1240 + 6710 into space could have been a short burst that no one had seen.

The study of fusion supernovae is a very wide field of research. We have plenty of observational evidence of supernova explosions in other galaxies. The problem, however, is that we can observe the stars just before the explosion, but it is very difficult for us to know their properties before it explodes. We are now discovering many different types of white dwarfs that have survived a supernova explosion under various conditions. Using the knowledge of their chemical composition, mass and speed, we can determine what kind of explosion survived. There is clearly a whole vast range of different supernovae. The study of such white dwarfs that survived the explosion in the Milky Way will allow us to understand a lot of other explosions observed in other galaxies - adds prof. Gaensicke.

An unusual explosion shot the star on a journey across the Milky Way


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