Irish astronomer helps measure black hole magnetic field for first time

Thursday 15 August 2013 13.56
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Artist's impression of a pulsar with a very high magnetic field (Pic: Ralph Eatough/MPIfR)
Artist's impression of a pulsar with a very high magnetic field (Pic: Ralph Eatough/MPIfR)
The Effelsberg radio telescope in Germany which is used to observe  the Galactic Centre region for unidentified pulsars (Pic: David Champion & Ralph Eatough/MPIfR)
The Effelsberg radio telescope in Germany which is used to observe the Galactic Centre region for unidentified pulsars (Pic: David Champion & Ralph Eatough/MPIfR)

An Irish astronomer is among an international group of researchers who have directly measured the magnetic field surrounding a black hole at the centre of our galaxy for the first time.

The research is published in the latest edition of the top scientific journal Nature.

It follows the discovery earlier this year of a special stellar beacon, or pulsar, near the "supermassive" black hole at the centre of our Milky Way galaxy.

For many years astronomers have been scanning the centre of the galaxy for pulsars.

A pulsar is a dying star which spins rapidly and emits a regular pulse of radio waves in the process.

Several months ago telescopes in space, which are operated by NASA, captured unusual X-ray bursts emanating from a pulsar at the centre of the galaxy.

Astronomers around the world quickly manoeuvred radio telescopes towards the pulsar and began taking readings.

"We were too excited to sleep in between observations! We were calculating flux densities at 6am on Saturday morning and we could not believe that this magnetar had just turned on so bright." said Irish astronomer, Dr Evan Keane, from the Jodrell Bank Observatory at the University of Manchester.

The radio waves were being twisted by a magnetic field created by gas clouds being sucked into the supermassive black hole at the centre of the Milky Way, called Sagittarius A*.

By analysing this twisting effect, the scientists have for the first time measured the strength of the magnetic field around the black hole and have concluded it is relatively strong.

Discovering a pulsar close to this black hole has been a key priority of astronomers for several decades.

Because the radio waves they emit are precisely timed, pulsars can be used for a variety of measurements, including testing Einstein's theory of relativity.

The pulsar used by the researchers in this paper is a magnetar, a rare type of pulsar with a magnetic field that is 1,000 times stronger than a normal pulsar, and 100 trillion times stronger than the magnetic field around earth.

Sagittarius A is slowly swallowing the hot, ionized gas around it through a process known as accretion. Yet the amount it devours is small in comparable to its size, and the question of why has puzzled scientists for some time.

The team was able to establish that the matter being eaten is surrounded by a magnetic field strong enough to regulate the black hole's consumption.

"There are really no other ways to measure these properties of supermassive black holes. So it really is an extreme laboratory for physics," Dr Evan Keane said.