Tripping the light fantastic: 66 black holes found 'dancing' the galactic night away



It is the ultimate dance routine but get too close and it may be your last.

A team of astronomers have discovered 33 pairs of 'waltzing' black holes in distant galaxies which will eventually combine to form one.

Nearly every galaxy has a central super-massive black hole with a mass up to a billion times the mass of the Sun and galaxies often collide.

Hubble Space Telescope images of two small galaxies colliding to form one

The resulting singular galaxy inherits two super-massive black holes which begin to perform a spiral dance around each other.



They gradually move towards the centre of the system and engage in a gravitational tug-of-war over nearby stars.

Eventually the same will happen to our own Milky Way when it collides with the Andromeda Galaxy - we'll all have ring-side seats in about three billion years.

The Hubble Space Telescopic snapped the final pairing of black holes

Dr Julia Comerford, from the University of California, announced the find using the Keck II Telescope in Hawaii and the Hubble Space Telescope which found the final pairing.

Astronomers expect many similar performances to be played out across the universe but only a handful have been found.

Dr Comerford said: 'Our result shows that such waltzing black holes are much more common than we previously knew.'

'We expect the universe to be littered with these waltzing black holes. But until recently, only a few had ever been found.'

Each black hole is powered by the gases seen collapsing into them. Dr Comerford and her team have also been using each pair to estimate how often galaxies merge.



They have concluded red galaxies originating between four and seven billion years ago were subject to three mergers around every billion years.

The discoveries help to alleviate the discrepancy between the expected and observed numbers of paired black holes in the universe and allow scientists to learn more about how galaxies merge and grow.

As each black hole appears red if it is moving away from the Earth and blue if it is approaching, the team looked for instances where there was one blue and one red in close proximity to each other.

The study, the DEEP2 Galaxy Redshift Survey, found 22 black hole pairs but was able to look only at those black holes which were sucking in gas and other materials from the surrounding environment as that's the only time they are visible.

The energy from the black hole heats up the gases, lighting it up in visible wavelengths, which are longer if the black hole is getting further away.

'It’s kind of the disco ball that tells you where the party is, where the black holes are dancing,” said Dr Comerford.

Both black holes move at around 200 kilometres per second but are separated on average by about 3,000 to 8,000 light-years - roughly one-eighth to one-third the distance from the sun to the centre of the Milky Way.

Two telescopes at the W.M. Keck Observatory on Mauna Kea in Hawaii

The Hubble Space Telescope found the final example of a galaxy merger, distinct because of its remarkable tail of stars, gas and dust.

'It’s like a black eye, a sign that this galaxy has recently gone through a collision with another galaxy.'

The newly-formed galaxy has two bright nuclei, potentially glowing dust and gas surrounding each of the black holes, but scientists are yet to be certain it is not actually a black hole which is escaping its galaxy due to the massive forces present when two black holes merge.

'Whether this thing is a dual pair of waltzing black holes or an ejected black hole, this is definitely a merger,' Comerford said. 'It’s just whether you’re seeing it before the black holes merge [with each other] or after.'