Aussie find a story written in the stars

So it is that an international team of astronomers has taken a step forward in understanding the evolution of galaxies. Or more precisely, how some of them obtained their central black hole.

Not quite feeling the love so far?

Over to the group's leader, Melbourne professor Alister Graham, who enthusiastically likens the new discovery to a tale of heavenly matrimony.

Anyway, the explanation goes like this:

Galaxies can have mutual gravitational attraction for each other. The body of a smaller one may fade over time but its heart remains intact as it falls into and partners with a larger galaxy.

In this case, the heart is a million-strong cluster of stars, seen with the Hubble Space Telescope near the centre of spiral galaxy NGC 4424.

The latter was already known to display signs of activity from a past merger event but Professor Graham and his team have discovered the remnant central star cluster of an in-falling galaxy with a black hole.

"The larger galaxy's bar-like structure is excited and buckled (because) there was also a star-forming event less than 500 million years ago," he explains.

"One can think of this as a star party of sorts, associated with the announcement of the upcoming galaxy wedding."

The Australian, who hails from Swinburne's Centre for Astrophysics and Supercomputing, concedes he has been branded a bit of a nerd for using the analogy.

Some say he might have been channelling Sheldon from TV's The Big Bang Theory when he thought of it.

It is something the professor is quick to counter, though, with the suggestion his discovery is indeed an important one for understanding the co-evolution of galaxies and black holes.

However this has not stopped his colleagues putting their own, somewhat less romantic spin on the cosmological event.

They have informally named the star cluster linked to NGC 4424 'Nikhuli'. It is a word used by the Sumi tribe of the Indian state of Nagaland for a festive period where descendants of head-hunters celebrate and wish for a rich harvest and gathering.

It seemed appropriate to the astronomers because they refer to space as 'the field' and the discovery focuses on how a larger galaxy has harvested a smaller one.

Co-author of the study, Professor Roberto Soria from the Chinese Academy of Sciences, obtained the Hubble image showing the high-energy X-ray source emanating from the stretched-out star cluster.

Although 50 million light-years from earth, radiation from the black hole bathes each square metre of the planet every 80 seconds, he says.

The team's best estimate for the mass of the gravitational field is seventy thousand times that of the sun.

Its research has been published in The Astrophysical Journal.

Australian Associated Press