Science Magazine reported on Thursday that astronomers have observed the fastest moving star ever recorded in our galaxy. Unlike other hypervelocity stars noticed so far, whose rapid movement was caused by the tremendous gravity of the black hole in the center of the Milky Way, this one was prompted on its trajectory towards the outskirts of our galaxy by a Type Ia supernova explosion. This kind of explosion is among the biggest and brightest cosmic energy-releases known to us.
The discovery of this record-breaking hypervelocity star named US 708 is very significant for astrophysicists because it helps them understand what causes a Type Ia supernova explosion. So far, there are three hypotheses that explain this kind of energy bursts. The first scenario is that a white dwarf, which results from the explosion of a red giant (a star that has reached the end of its normal-activity cycle and inflates its volume, until it finally sheds off its outer layers), gains enough matter (from a companion star, for instance) to reach a critical point where it detonate in a thermonuclear explosion. The second possibility is that a Type Ia supernova is born out of the collision of two white dwarfs. Finally, another explanation, discovered relatively recent in 2013, is that thermonuclear explosions of this sort are caused by systems formed of a white dwarf closely orbiting a hot helium-rich subdwarf. Helium falling onto a white dwarf can provoke a Type Ia explosion.
US 708 was such a hot subdwarf, spotted with strongly magnifying Keck telescopes by the astrophysicists at the European Southern Observatory, led by Stefan Geier. Aside from noticing the incredible speed of the star (2.6 million miles per hour, which is about 4.2 million kilometers per hour), the scientists calculated its trajectory, which indicated that the star had not come from the central black hole of the galaxy. This meant that it probably came from a Type Ia explosion – a fact confirmed by its fast rotating movement, typical for stars that recently came out of the tight gravitational field of a companion-star.
To get a hint of the importance of this event for astrophysicists, we must take into consideration that Type Ia supernovae are some of the brightest phenomena in the universe, used to calculate the extent of the gaps between us and very distant galaxies, as well as the speed with which that gap is increasing. Because this speed is not constant, but rising in its turn (galaxies move away from each other faster and faster), understanding cosmic expansion is tightly related with understanding what causes Type Ia supernovae and calculating how much energy they generate.
image source: Yibada