Chinese astrophysicists discovered the fastest rotating star of the Milky Way

The fastest rotating star in the Milky Way belongs to the spectral class O6.5 - these are hot blue stars
The fastest rotating star in the Milky Way belongs to the spectral class O6.5 - these are hot blue stars

The star LAMOST J040643.69 + 542347.8 is located in the outer arm of the Milky Way.

Astrophysicists discovered the fastest spinning star in the Milky Way Galaxy. Its distance of about 30 thousand light years from the Sun, and its upper layers rotate at a record high speed.

About 540 kilometers per second, which is 100 kilometers per second faster than the previous record holder HD 191423. Astrophysicist Guang-Wei Li writes a preprint on about the results of spectroscopic observations that made this conclusion.

Stars rotate around their axis from the moment of birth – as the gas cloud collapses into the protostar, the angular momentum is conserved, which leads to rapid rotation.

Gradually, this rotation slows down as a result of the interaction of the magnetic field of a star with a stellar wind.

A point on the equator of the Sun moves at a speed of just over two kilometers per second. However, there are stars that spin extremely fast.

Fastest rotating star in the Milky Way

The fastest currently known VFTS 285 and VFTS 102 in the Large Magellanic Cloud rotate at a speed of about 610 kilometers per second.

In our Galaxy, until recently, the rotation speed record belonged to HD 191423 – 435 kilometers per second. The actual rotation speed of these stars can be even greater – because we can only measure speed in projection onto the line of sight.

Rotating so fast it is not easy for a star.

Usually in the Milky Way fast-spinning stars are in binary systems and owe high speed to their companions with whom they actively exchange matter.

They can be the source of such an interesting phenomenon as long gamma-ray bursts. In addition, rapid rotation dramatically affects the circulation of matter inside the star.

It mixes – hydrogen transferred to the core, products of the carbon-nitrogen-oxygen cycle – to the surface, which increases the star’s lifespan and luminosity.

Guang-Wei Li calls the discovery of the fastest rotating star in the Galaxy a lucky coincidence.

Discovered during the search using the LAMOST spectroscopic telescope. Class O stars are hot blue stars with hydrogen emission lines. The spectral class LAMOST J040643.69 + 542347.8 was defined as O6.5. Unusually wide lines in the spectrum indicated a fast rotation of the star.

From the edge of a star approaching us, all lines of the spectrum shift to the blue part of the spectrum, from the moving away to the red part, and as a result of addition, the spectral lines become wider the faster they rotate.

To measure rotation speed, the author used the absorption line of ionized helium He II λ4542 – it forms deep inside the photosphere and stellar wind does not affect it anymore.

Turned out that the rotation speed of the upper layers of the star in projection onto the line of sight is approximately 540 kilometers per second.

The star rotation is 100 kilometers per second faster than that found in 2001, HD 191423.

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