Universe Guide

Sagittarius A*, Galactic Centre of the Milky Way Galaxy

Sagittarius A* Facts

Information on Sagittarius A*

It is the centre by which all stars in the galaxy orbit round. Our Solar System is travelling at an average velocity of 828,000 km/hr. Bet you thought the Sun stood still and we just orbited round it. Even with that speed, it takes the solar system to orbit round the centre a total of 230 Million Years give or or take a few millenias and more. The Galactic Centre has a mass of about 200 million times that of the Sun. Based on analysis of stars and other galaxies, it is believed we are in the Orion arm of the solar system. N.A.S.A

Discovery of Sagittarius A*

It was a team at Dover Height in Australia that calculated the location of Sagittarius A*. A team from Commonwealth Scientific and Industrial Research Organisation (CSIRO) led by Joseph Lade Pawsey used Sea Interferometry where radio signals are reflected off water to measure the radio waves. They detected a number of interstellar and intergalactic radio sources including Taurus A*, Virgo A* and Centaurus A*. When they discovered Sagittarius A*, they discovered it was very close to where the centre of the galaxy was located. Wiki

The centre of the galaxy was calculated by Jan Oort, a famous Dutch astronomer. He was able to calculate how far we are from the galactic centre and how long it would take to orbit the galactic centre. Jan Oort is more famous for theorizing the existence of the Oort Cloud, the hypothetical location of a spherical cloud of where comets come from. Wiki.

Picture of Sagittarius A* taken by the Chandra X-Ray Observatory

Sagittarius constellation

Its name gives its location away, it is in the constellation of Sagittarius, the archer. All those who believe in Astrology will be chuffed to have the centre of the galaxy, our galaxy within its borders. Sagittarius A* is located near the border with Scorpius so it could quite easily have gone the other way.

When the constellation maps were drawn up, it was not known at that time where the location of the centre of the galaxy was. Had they known about the location, sighting the black hole in Sagittarius would have been controversial. To appease both groups, they would probably have placed the centre in the constellation of Ophiuchus so neither party would get the upper hand.

Anti-Centre of the Galaxy

Whilst we are talking about the centre, lets talk about the location of the anti-centre of the galaxy. The Anti-Centre is the location of the galaxy that if we were aiming to go in the opposite direction of the centre of the galaxy we would go in. The anti-centre is near the Taurus star Elnath near the border with Gemini, the constellation of the twins.

The Anti-centre is not the quickest way out of the galaxy. The quickest way out of the galaxy would be to go up because the Galaxy is a disk rather than a ball. You'd probably want to head towards Arcturus, Alpha Bootes or more precisely a location in the Coma Berenices constellation if you wanna get out quick.

What is it like at Sagittarius A*

The area around the Black Hole is not a very nice place, it is an area of super-heated gas that extends light years away from the centre. The area is about 20 million degrees Celsius. It is an area that is extremely violent with sporadic explosions and flaring. Jets of particles travelling at the speed of light are emanating out from the Event Horizon. Despite this, there is evidence that a star is orbiting very close to Sagittarius A*. Cornell

Giant and Hypervelocity Stars

Some stars have been known to get to close to the centre of the galaxy and be forcibily ejected out of the galaxy. One such star is SDSS J090745.0+024507 which is currently speeding out of the galaxy having been sent on its path by a close interaction with Sagittarius A. It is possible that the cause of the Hypervelocity Star is that it a companion star or stars were sucked into the Supermassive Black Hole causing the star to start its journey.

There are a number of giant stars clustered near or in the general direction of the Galactic Centre. There's none more famous that the reputed largest known star in the universe and it is at 1,708 times as large as our Sun, UY Scuti.

Sagittarius A*, Galactic Centre of the Milky Way Galaxy's Alternative Names

Sagittarius A*, Galactic Centre of the Milky Way Galaxy has alternative name(s) :- Sgr A*.

More details on objects' alternative names can be found at Star Names .

Location of Sagittarius A*

The location of the supermassive black hole in the night sky is determined by the Right Ascension (R.A.) and Declination (Dec.), these are equivalent to the Longitude and Latitude on the Earth. The Right Ascension is how far expressed in time (hh:mm:ss) the star is along the celestial equator. If the R.A. is positive then its eastwards. The Declination is how far north or south the object is compared to the celestial equator and is expressed in degrees. For Sagittarius A*, the location is 17h 45m 40.036 and -29° 00` 28.17 .

Distance to Sagittarius A*

Sagittarius A* is an estimated 25,896.82 light years from our Solar System (Earth and Sun). It would take a spaceship 25,896.82 years travelling at the speed of light to get there. We don't have a space ship that can travel that distance or at that speed yet.

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Additional Sagittarius A* Facts and Figures

Visual Facts

Primary / Proper / Traditional NameSagittarius A*, Galactic Centre of the Milky Way Galaxy
Alternative NamesSgr A*
Constellation's Main StarNo
Multiple Star SystemNo / Unknown
Star TypeSupermassive Black Hole
GalaxyMilky Way
Right Ascension (R.A.)17h 45m 40.036
Declination (Dec.)-29° 00` 28.17
Distance from the Sun / Earth25,896.82 Light Years

Companions (Multi-Star and Exoplanets) Facts

Exoplanet CountNone/Unaware

Sources and Links


Location of Sagittarius A* in Sagittarius

Sagittarius A* Location in Sagittarius

The map was generated using Night Vision, an awesome free application by Brian Simpson.

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