One of the weirdest and most fascinating objects in the universe are black holes and the king of the black holes are the Super Massive Black Holes (SMBH). In our galaxy we are lucky enough to have one right in the middle, infact most galaxies appear to have one at their centres. The beauty of our SMBH is that we can observe it, sort of. The monster at the centre of our galaxy is called Sagittarius A*. Basically we can observe what is happening around it and right now there’s a lot going on around our pet SMBH. One of the things that such a massive and wild object can allow scientists to do is test Einstein’s theory of General Relativity.
Last year, a group of scientists from the Czech Republic and Germany lead by Andreas Eckart from the University of Cologne observed three stars that were getting a bit close to the SMBH at the centre of our galaxy to see if they could confirm the theory of general realivity, which basically states that something big enough will bend space/time enough so it can be measured. The three stars that the team looked at are called S stars and there’s a bunch of them whizz around the SMBH, some of them get to within a 100 AU of the monster (an AU is th distance between the Earth and the Sun). The SMBH is so massive that it weighs about as much as 4 million Suns so it’s massive gravitational effect can speed up the stars orbiting it to some truly impressive speeds. The stars that the team observed get up to 1-2% of the speed of light.
They used data from the Very Large Telescope in Chile and tracked the movement of the stars as they tracked around the SMBH. They observed that one of the stars, known as S2 showed some deviations in it’s orbit. These deviations might be an indicator of relativistic effects and could be further proof of Einsteins theory of general realivity. Luckily there’s another chance to make some measurements of a star getting up close and personal with our SMBH. What scientists are expecting to see is a red shift of the stars signature and a deviation in the orbit. The star that is going to be observed is called S0-2 and it’s one of two that get the closest to the SMBH.
During its closest approach S0-2 will get to within a distance that is the equivalent of about four times the distance between Neptune and the Sun (about 17 light hours). The star will accelerate to around 3% of the speed of light and give one of th best chances to confirm the observations of last year’s team and to test the theory of general relativity. Astronomers are hoping that the S0-2 is not a binary star as that could complicate the calculations but observations so far suggest that the star probably doesn’t have a binary and even if it did it probably wouldn’t be big enough to have an effect on any deviations.
The existence of the SMBH at the centre of our galaxy hasn’t always been known about and it was only in 2002 when a team of astronomers who were tracking the S stars at the centre of the galaxy had collected enough data to pin point that a huge gravitational source was at the centre of their orbits. More data was collected and by 2008 27 stars had been mapped so the position and size of the SMBH was able to be estimated more accurately. The current estimation is the SMBH is at 4.31 million solar masses. Calculations suggest that the event horizon for this monster is 15.4 million kms – about 11 times the diameter of the Sun. Further observations have led scientists to estimate that the massive black hole is spinning at about 30% of the speed of light, meaning it does one rotation every 11 minutes. The image at the top of the article is an x-ray image of the area around Sagittarius A* from NASA.
This is a fascinating object at the centre of our galaxy and will no doubt continue to give up its secrets.