Colliding Black Holes and the Dawn of Gravitational Astronomy

New simulations of the most energetic collisions in the universe are helping astrophysicists understand how gravitational waves are generated, possibly giving us an exciting glimpse into the future of gravitational astronomy.

New simulations of the most energetic collisions in the universe are helping astrophysicists understand how gravitational waves are generated, possibly giving us an exciting glimpse into the future of gravitational astronomy.

Black hole mergers are thought to be the most energetic events the universe has seen since the Big Bang, nearly 14 billion years ago. These events occur when two (or more) spinning black holes become trapped in their mutual gravitational wells, orbit and then collide, merging as one. The energy generated in these merging events are thought to create a very specific signature of gravitational wave emissions.

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According to Einstein's theory of general relativity, gravitational waves should be created when massive objects accelerate through space. However, they have not been directly observed. Indirectly, we can see their impact when white dwarf binaries, for example, orbit one another - over time, as their orbits shrink, energy is lost. This energy must be carried away from the system by gravitational waves.

Although we have a pretty good idea about their properties, gravitational waves are notoriously difficult to detect directly, but should they become detectable in the future, a new era of gravitational astronomy may be possible. And black hole mergers could be the key to making this happen.

"An accelerating charge, like an electron, produces electromagnetic radiation, including visible light waves," Michael Kesden, of the University of Texas at Dallas, said in a press release. "Similarly, any time you have an accelerating mass, you can produce gravitational waves."

Kesden is the lead author of new research into black hole mergers published in the journal Physical Review Letters.

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"Using gravitational waves as an observational tool, you could learn about the characteristics of the black holes that were emitting those waves billions of years ago, information such as their masses and mass ratios, and the way they formed," added co-author Davide Gerosa, of the University of Cambridge, UK. "That's important data for more fully understanding the evolution and nature of the universe."

Currently, there are several projects underway that are attempting to detect gravitational waves. Perhaps the most famous detector is the Laser Interferometer Gravitational-Wave Observatory (LIGO) situated at two locations in the US - in Louisiana and Washington. LIGO is set up to detect the passage of gravitational waves through our local volume of space.

Using precision lasers along two 4 kilometer-long tunnels in "L" shaped structures, the very slight perturbations of spacetime should be detectable as gravitational waves pass through our planet. Although LIGO has yet to detect a positive gravitational wave signal, it is currently undergoing upgrades that will boost its sensitivity. "Advanced LIGO" is scheduled to go online later this year. Europe is also building its own detector called VIRGO and the LISA Pathfinder Mission is planned to set up a gravitational wave detector in space.

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"The equations that we solved will help predict the characteristics of the gravitational waves that LIGO would expect to see from binary black hole mergers," said co-author Ulrich Sperhake, also of the University of Cambridge. "We're looking forward to comparing our solutions to the data that LIGO collects."

The researchers have specifically focused on modelling the spin and precession of binary black holes as they orbit one another.

"Like a spinning top, black hole binaries change their direction of rotation over time, a phenomenon known as procession," said Sperhake. "The behavior of these black hole spins is a key part of understanding their evolution."

"With these solutions, we can create computer simulations that follow black hole evolution over billions of years," said Kesden. "A simulation that previously would have taken years can now be done in seconds. But it's not just faster. There are things that we can learn from these simulations that we just couldn't learn any other way."

The researchers hope that, with the help of their computer models, new details behind black hole mergers may be revealed. In doing so, the specific gravitational wave signal may be characterized so that when detectors such as Advanced LIGO register their first signals, we may quickly untangle what is generating the emission.

Like optical astronomy revolutionized our naked eye view on the universe and X-ray astronomy highlighted some of the most energetic phenomena in the cosmos, gravitational wave astronomy could give us a view of a previously invisible realm - a realm of massive interactions and collisions that characterize the very evolution of our universe.

Source: University of Cambridge

This image of the galaxy NGC 6240 contains X-ray data from Chandra (shown in red, orange, and yellow) that has been combined with an optical image from the Hubble Space Telescope originally released in 2008. In 2002, the discovery of two merging black holes was announced based on Chandra data in this galaxy. The two black holes are a mere 3,000 light years apart and are seen as the bright point-like sources in the middle of the image.

Using data from the Hubble Space Telescope's famous Ultra-Deep Field (UDF) observation,

astronomers have been able to deduce at what age spiral galaxies acquire their spiral structure

. Since its launch in 1990, the veteran observatory has studied countless galaxies, but some of the most striking images are that of the majestic spirals that pervade the entire observable universe. In this celebration of spiral galaxies and Hubble's prowess at imaging them, we've collected some of our favorite galactic views from the space telescope's archives.

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In this majestic image, phenomenal detail in galaxy

NGC 2841

's spiraling dust lanes have been captured.

Spiral galaxy

NGC 5866

as seen nearly edge-on from Hubble's perspective. The dark galactic dust silhouettes the bright galactic core.


unnamed spiral galaxy

located deep within the Coma Cluster of galaxies, around 320 million light-years away in the northern constellation Coma Berenices, shows off some intricate detail in its arms.

The famous

Sombrero galaxy

(Messier 104) is an edge-on spiral galaxy -- the "rim" of the sombrero is thick lanes of dust obscuring the galaxy's starlight.


is another spiral galaxy not too dissimilar to our Milky Way. Young, bluish stars track along the galaxy's majestic arms, while older, redder stars cluster in its bright core.

This unique view of


is a combination of Hubble data and photographs taken by astrophotographer Robert Gendler.

The 'classic' spiral

Whirlpool Galaxy

gravitationally interacts with a neighboring galaxy, refining its very clear spiral arms.

To celebrate Hubble's 21st year in space, astronomers released this striking image of a pair of interacting galaxies called

Arp 273

. (Image rotated)

The 3 galaxies of

Arp 274

appear to be very close to one another, but astronomers believe that they are far apart and only overlapping from our perspective.


UGC 10214

is undergoing some violent gravitational disturbances after a suspected galactic collision. The creation of the stream of stars post-collision appear as a tail, giving the galaxy "The Tadpole" moniker.

To see full-resolution images and more detail on the galaxies showcased here, browse the mindblowing online Hubble album.