- Unusual objects that look like gas and behave like stars found near Sagittarius A*
- They look compact but stretch out when orbits bring them closer to black hole
- The gas cloud’s orbits around Sagittarius A* range from about 100 to 1,000 years
Orbits of the G objects at the centre of our galaxy, with the supermassive black hole indicated with a white cross. Stars, gas and dust are in the background
The dusty cloud G2 as it closes in on, and then passes, the supermassive black hole at the centre of the Milky Way. The different colours mark the position of G2 in the years 2006, 2010, 2012 and February and September 2014, from left to right, with the supermassive black hole marked by the red cross
Unusual objects that look like gas and behave like stars have been spotted near our galaxy’s enormous black hole, astronomers have said.
Four new discoveries have been found closely orbiting a supermassive black hole called Sagittarius A* located 26,000 light years away from Earth.
They join G1 and G2, which were found in 2005 and 2012 respectively, intriguing scientists because they seem to be compact most of the time but stretch out as they get closer to the black hole during their orbit.
The orbits of these bizarre celestial bodies can take between 100 and 1,000 years.
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Researchers at the University of California, Los Angeles, have fittingly named the newcomers G3, G4, G5 and G6.
Writing in the journal Nature, the group explained its belief that all six were once binary stars – a pair of stars which orbit each other – later merging as one due to the supermassive black hole’s powerful gravitational force.
However, this merging process is not done overnight – it takes more than one million years to complete, said co-author Andrea Ghez.
‘Mergers of stars may be happening in the universe more often than we thought, and likely are quite common,’ she explained.
‘Black holes may be driving binary stars to merge. It’s possible that many of the stars we’ve been watching and not understanding may be the end product of mergers that are calm now.
‘We are learning how galaxies and black holes evolve. The way binary stars interact with each other and with the black hole is very different from how single stars interact with other single stars and with the black hole.’
Ghez’s research group identified an unusual object at the centre of our galaxy in 2005, which was later named G1.
In 2012, astronomers in Germany made a puzzling discovery of a bizarre object named G2 in the centre of the Milky Way.
G2 is most likely two stars that had been orbiting the black hole in tandem and merged into an extremely large star, cloaked in unusually thick gas and dust.
‘At the time of closest approach, G2 had a really strange signature,’ Ghez said.
‘We had seen it before, but it didn’t look too peculiar until it got close to the black hole and became elongated, and much of its gas was torn apart.
‘It went from being a pretty innocuous object when it was far from the black hole to one that was really stretched out and distorted at its closest approach and lost its outer shell, and now it’s getting more compact again.’
While G1 and G2 have similar orbits, the four new objects have very different orbits, which range from about 100 to 1,000 years.
The team is already looking into other potential objects that may be part of the same family.
It says the research will help shine a light on what is happening in the majority of galaxies in our universe – though Earth is quite a distance from the action, ‘in the suburbs compared to the centre of the galaxy’, Ghez said.
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.