• South Africa's huge optical telescope, SALT, has just helped astronomers find a high-speed star racing through the galaxy.
  • The white dwarf is travelling between 1,000km/s and 2,500km/s.
  • Scientists believe its the surviving partner of a pair of stars that was flung across the galaxy once it escaped the gravitational pull of its neighbour, after it exploded. 


South Africa's huge optical telescope, SALT, has just helped astronomers find a high-speed star racing through the galaxy.

The discovery has helped researchers better understand how supernovae occur.

There are between 150 billion and 250 billion stars in the Milky Way Galaxy and the high- speed white dwarf was discovered using data from Gaia Sky and the SALT (South African Large Telescope).

"Runaway white dwarfs like these are not very common, because of their brightness, we cannot detect them beyond about 3,000 light years away. Within that radius, we expect of order 20 or so,” said Dr Daniel Cunnama, South African Astronomical Observatory Science Engagement Astronomer. 

"In this case, seven candidate stars were detected in the Gaia data and were followed up using SALT and three other telescopes, three high-velocity white dwarf stars were detected,"

The white dwarf is travelling fast.

A bullet from a high-powered rifle can reach a velocity of 1,700 metres per second (m/s); a meteor can easily hit 11 kilometres per second (km/s), but this white dwarf is racing at between 1,000km/s and 2,500km/s.

But at speed though, it is unlikely to hit the Earth.

"The high-velocities seem to originate from a system that went supernova, ejecting the stars across the galaxy. It is extremely unlikely that they would impact the Earth; the Earth is a very, very small target on the scale of the galaxy," said Cunnama.

In binary star systems, two stars orbit each other.

Scientists postulate that when one star explodes in a violent supernova, the surviving partner star may be flung across the galaxy once it escaped the gravitational pull of its neighbour.

Data from SALT found a surviving star dubbed the "dynamically driven double-degenerate double-detonation" (D6) scenario.

Planets

These stars have "a lack of hydrogen and strong signatures of carbon, oxygen, and magnesium, as well as luminosities and temperatures unlike almost all other stars", say the researchers.

Data also establishes that the past location of the star coincides with the location of a supernova.

According to Space.com, astronomers first observed a high-speed star flying out of the Milky Way at 40,000km/s in 2005.

Researchers surmised that in 10% of cases, even the planets of these stars would remain bound as the star was flung through the galaxy. In some cases, planets also get expelled from the system, becoming high speed planets which have no host star.

The team undertaking the observations and data analysis was led by University of California at Berkeley Ken Shen. The SALT observations were taken by Marissa Kotze at the SAAO as part of a programme led by Saurabh Jha from Rutgers, the State University of New Jersey.

"This work highlights how we contribute to high impact science from the African continent through strong collaborations with our international partners. Our facilities are perfectly equipped and situated to do follow-up observations on potentially interesting astronomical objects that are identified by large survey missions," said Kotze.

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