Astronomy Now Home
Home Magazine Resources Store

On Sale Now!



The October 2014 issue of Astronomy Now is on sale! Order direct from our store (free 1st class post & to UK addresses). Astronomy Now is the only astronomy magazine specially designed to be read on tablets and phones. Download the app from Google Play Store or the Apple App Store.



Top Stories



Earthshine used to test life detection method
...By imagining the Earth as an exoplanet, scientists observing our planet's reflected light on the Moon with ESO's Very Large Telescope have demonstrated a way to detect life on other worlds...
  READ MORE

Solid buckyballs discovered in space
...Astronomers using NASA’s Spitzer Space Telescope have detected a particular type of molecule, given the nickname “buckyball”, in a solid form for the first time...
  READ MORE

Steamy water-world gets the Hubble treatment
...Hubble Space Telescope observations of a 7 Earth-mass planet find an unusual water-rich world swathed in a thick, steamy atmosphere...
  READ MORE








M87’s black holes gets its kicks from merger
KEITH COOPER
ASTRONOMY NOW
Posted: 26 May 2010


Bookmark and Share

The supermassive black hole at the centre of the giant galaxy M87 isn’t where it is supposed to be, according to new findings presented yesterday at the American Astronomical Society’s 216th meeting in Miami. Measurements indicate that it has been kicked 71 light years from the centre of M87 by a merger with another black hole.

Messier 87, at the heart of the Virgo Cluster, is a giant elliptical galaxy, one of the biggest in the Universe, and inside it is an immense black hole 6.4 billion times more massive than our Sun. The galaxy and its supermassive black hole grew to such gigantic sizes because of mergers with other galaxies and their black holes.

The central regions of M87, including its powerful relativistic jet. The jet is emanating from around the black hole. Image: NASA/Hubble Heritage Team (STScI/AURA).

A feature of elliptical galaxies is that they show a smooth decrease in brightness radiating away from their centre. A team led by Dr Daniel Batcheldor of the Florida Institute of Technology measured the isophotes – lines of constant brightness, akin to geographical contour lines – which centre on the topographical centre of M87. There they should have found M87’s black hole, but they found it had been offset by 71 light years. Not only does this put into question the assumption that black holes are always at the very centre of black holes, it also raises questions of what caused this state of events in the first place. Batcheldor’s team drew up four possible scenarios, including a binary black hole system, perturbations by the total gravity of the surrounding system of globular clusters, and recoil from M87’s famous jet of energy blasting out from the black hole at nearly the speed of light, before settling on what they believe is the most likely explanation: that the black hole was involved in a merger at some point in its history that gave it a kick away from M87’s centre.

They arrived at this conclusion partly because it has its own merits – galaxy mergers result in a gravitational kick that propels the black hole away from the galaxy – but also by ruling out the other possible explanations. “If it were produced by a supermassive black hole binary system, we would expect to see the second black hole exactly symmetrically opposite, and it would have a similar mass, but we see no evidence for it,” says Batcheldor. And although M87’s jet appears to be one-sided, theoretical models of such jets describe two jets blasting out in opposite directions, so although we can’t clearly see a second jet hidden behind M87, astronomers assume it is there (and there is tentative evidence for it) and this would neutralise any recoil. As for the globular clusters, of which there is over a whopping 10,000, their cumulative gravitational influence would only be able to nudge the black hole 0.3 light years. Thus a black hole merger appears to be the only viable explanation.

The size of the black hole with which it merged, and how long ago this happened, remains unknown. “One thing we’re lacking is its velocity,” says Batcheldor. “Without that information we cannot tell when it occurred. An analogy is an olive in a salad bowl. If you give it a flick it oscillates up and down the bowl, but if you observe that at any point you wouldn’t be able to tell when it was flicked. It could have happened anytime in the last ten billion years, and without knowing that we can’t extrapolate back to find the pre-merger mass ratio between the black holes.”

This isn’t the first time we’ve seen black holes get a kick from a merger, but in those cases the black holes have been shoved thousands of light years from the centre of their galaxy. Messier 87’s black hole is the smallest offset of any black hole ever seen, and its journey could be only just beginning – it may take millions or billions of years to return to rest.

The Planets
From tiny Mercury to distant Neptune and Pluto, The Planets profiles each of the Solar System's members in depth, featuring the latest imagery from space missions. The tallest mountains, the deepest canyons, the strongest winds, raging atmospheric storms, terrain studded with craters and vast worlds of ice are just some of the sights you'll see on this 100-page tour of the planets.
 GET YOUR COPY

Hubble Reborn
Hubble Reborn takes the reader on a journey through the Universe with spectacular full-colour pictures of galaxies, nebulae, planets and stars as seen through Hubble's eyes, along the way telling the dramatic story of the space telescope, including interviews with key scientists and astronauts.
 GET YOUR COPY

3D Universe
Witness the most awesome sights of the Universe as they were meant to be seen in this 100-page extravaganza of planets, galaxies and star-scapes, all in 3D!
 GET YOUR COPY


HOME | NEWS ARCHIVE | MAGAZINE | SOLAR SYSTEM | SKY CHART | RESOURCES | STORE | SPACEFLIGHT NOW

© 2014 Pole Star Publications Ltd.