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Astronomers discover fastest spinning white dwarf star ever observed

An artist’s impression of the fastest spinning confirmed white dwarf and only second ever magnetic propeller known. (Credits: PA)

Astronomers have discovered the fastest spinning white dwarf star ever observed.

The white dwarf star completes a full rotation once every 25 seconds, researchers said.

They have established the spin period of the star for the first time, confirming it as an extremely rare example of a magnetic propeller system.

This is when the white dwarf is pulling material from a nearby companion star and flinging it into space at around 3,000 kilometres per second.

University of Warwick astronomers report it is only the second magnetic propeller white dwarf to have been identified in more than 70 years.

This was done using a combination of powerful and sensitive instruments that allowed scientists to catch a glimpse of the speeding star.

A white dwarf is a star that has burnt up all of its fuel and shed its outer layers, and is now in the process of shrinking and cooling over millions of years.

The star the Warwick team observed, named LAMOST J024048.51+195226.9 – or J0240+1952 for short, is the size of the Earth but is thought to be at least 200,000 times more massive.

It is part of a star system and its immense gravity is pulling material from its larger companion star in the form of plasma.

In the past, this plasma was falling onto the white dwarf’s equator at high speed, providing the energy that has given it this dizzyingly fast spin.

In comparison, one rotation of the Earth takes 24 hours while on J0240+1952 it takes just 25 seconds.

That is almost 20% faster than the confirmed white dwarf with the most comparable spin rate, which completes a rotation in just over 29 seconds.

At some point in its evolutionary history J0240+1952 developed a strong magnetic field.

It acts as a protective barrier, causing most of the falling plasma to be propelled away from the white dwarf. What is left will flow towards the star’s magnetic poles.

Artist’s impression of a white dwarf surrounded by clouds of gas (Nasa)

Lead author Dr Ingrid Pelisoli, of the University of Warwick Department of Physics, said: ‘J0240+1952 will have completed several rotations in the short amount of time that people take to read about it, it is really incredible.

‘The rotation is so fast that the white dwarf must have an above average mass just to stay together and not be torn apart.

‘It is pulling material from its companion star due to its gravitational effect, but as that gets closer to the white dwarf the magnetic field starts to dominate.

‘This type of gas is highly conducting and picks up a lot of speed from this process, which propels it away from the star and out into space.’

Co-author Professor Tom Marsh, from the University of Warwick Department of Physics, said: ‘It’s only the second time that we have found one of these magnetic propeller systems, so we now know it’s not a unique occurrence.

‘It establishes that the magnetic propeller mechanism is a generic property that operates in these binaries, if the circumstances are right.

‘The second discovery is almost as important as the first as you develop a model for the first and with the second you can test it to see if that model works.

‘This latest discovery has shown that the model works really well, it predicted that the star had to be spinning fast, and indeed it does.’

The study, published in Monthly Notices of the Royal Astronomical Society: Letters, was led by the University of Warwick with the University of Sheffield, and funded by the Science and Technology Facilities Council (STFC), part of UK Research and Innovation, and the Leverhulme Trust.

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