‘Runaway star’ ejected from the black hole at the centre of our galaxy is spotted travelling at 3.7million miles per hour on its way out of the Milky Way

  • The star is called S5-HVS1 and was discovered in the Grus constellation, which is also known as the Crane
  • It is travelling at more than ten times faster than most of the other stars move in the Milky Way galaxy
  • It was ejected by Sagittarius A*, the supermassive black hole situated at the centre of our galaxy
  • S5-HVS1 was discovered using the 3.9-metre Anglo-Australian Telescope with help from the Gaia satellite

A ‘runaway star’ has been discovered racing away from the heart of the Milky Way ten times faster than most of the other stars in the galaxy.

The star, called S5-HVS1 was found 29,000 light years from Earth travelling at more than 3.7million miles per hour.

It was ejected by the supermassive black hole at the heart of the galaxy five million years ago – around the time human ancestors were learning to walk on two feet. 

Scientists think the star was part of a binary system. The pair got too close to the supermassive black hole at the centre of the galaxy – as seen in this artist illustration – and while one was pulled in the other was pushed out

The star was found in the constellation of Grus – or the Crane –  by Sergey Koposov from Carnegie Mellon University and the Southern Stellar Stream Spectroscopic Survey.

‘This is super exciting as we have long suspected that black holes can eject stars with very high velocities. 

‘However, we never before had a clear association of such a fast star with the Galactic Centre’, he said. 

Scientists say S5-HVS1 is unprecedented due to its high speed and relatively close passage to the Earth. 

The team behind the discover say it has been ejected from the galactic centre, pictured, and based on the stars current trajectory and the incredible speed it is travelling it will leave the Milky Way and never return

The runaway star is thought to have left the galactic centre about 5million years ago when early humans were just learning to stand on two feet

Scientists say S5-HVS1 is unprecedented due to its high speed and relatively close passage to the Earth. It was found about 29,000 light years from us 

The trajectory it is on and the speed it is going means that it will leave the Milky Way and never return, the team confirmed.


Black holes are so dense and their gravitational pull is so strong that no form of radiation can escape them – not even light.

They act as intense sources of gravity which hoover up dust and gas around them. Their intense gravitational pull is thought to be what stars in galaxies orbit around.

How they are formed is still poorly understood. Astronomers believe they may form when a large cloud of gas up to 100,000 times bigger than the sun, collapses into a black hole.

Many of these black hole seeds then merge to form much larger supermassive black holes, which are found at the centre of every known massive galaxy.

Alternatively, a supermassive black hole seed could come from a giant star, about 100 times the sun’s mass, that ultimately forms into a black hole after it runs out of fuel and collapses.

When these giant stars die, they also go ‘supernova’, a huge explosion that expels the matter from the outer layers of the star into deep space.

They were able to use its speed and distance from Earth to determine it had to have been ejected by Sagittarius A*, the name for the Milky Way’s supermassive black hole, which is four million times the size of our sun.

‘Seeing this star is really amazing as we know it must have formed in the Galactic Centre, a place very different to our local environment’, said Ting Li, from Carnegie Observatories.

‘It is a visitor from a strange land,’ she said.

S5-HVS1 is an A-type star, which is a young star that is likely only a few hundred million years old. Our sun is 4.6billion years old.

The surface temperatures of A-type stars range from 13,000 Fahrenheit to about 18,000 Fahrenheit.

Our sun, which is a yellow dwarf star has a surface temperature of 9,940 Fahrenheit. 

The speeding star was discovered using the 3.9-metre Anglo-Australian Telescope near Coonabarabran, New South Wales, Australia.

Observations from the European Space Agency’s Gaia satellite were also used to allowed the astronomers to reveal the full speed of the star and its journey. 

Scientists think that S5-HSV1 originally lived with a companion in a binary system, but they strayed too close to Sagittarius A*. 

In the gravitational tussle, the companion star was captured by the black hole while S5-HVS1 was thrown out at extremely high speed, a process known as the Hills Mechanism, proposed by astronomer Jack Hills 30 years ago.

The star is expected to leave the Milky Way completely and head into intergalactic space as it is moving at millions of miles per hour


The Galactic centre of the Milky Way is dominated by one resident, the supermassive black hole known as Sagittarius A* (Sgr A*).

Supermassive black holes are incredibly dense areas in the centre of galaxies with masses that can be billions of times that of the sun.

They act as intense sources of gravity which hoover up dust and gas around them. 

Evidence of a black hole at the centre of our galaxy was first presented by physicist Karl Jansky in 1931, when he discovered radio waves coming from the region. 

Pre-eminent yet invisible, Sgr A* has the mass equivalent to some four million suns.  

At just 26,000 light years from Earth, Sgr A* is one of very few black holes in the universe where we can actually witness the flow of matter nearby.

Less than one per cent of the material initially within the black hole’s gravitational influence reaches the event horizon, or point of no return, because much of it is ejected. 

Consequently, the X-ray emission from material near Sgr A* is remarkably faint, like that of most of the giant black holes in galaxies in the nearby universe.

The captured material needs to lose heat and angular momentum before being able to plunge into the black hole. The ejection of matter allows this loss to occur.

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