ANDREA GHEZ .... first to prove existence of blackhole in centre of our galaxy

                                              (above video is of Andrea Ghez on TED)

Seeing the unseen (from 26,000 light-years away) is a specialty of UCLA astronomer Andrea Ghez. From the highest and coldest mountaintop of Hawaii, home of the Keck Observatory telescopes, using bleeding-edge deep-space-scrying technology, Ghez handily confirmed 30 years of suspicions of what lies at the heart of the Milky Way galaxy -- a supermassive black hole, which sends its satellite stars spinning in orbits approaching the speed of light. 

Ghez received a MacArthur "genius grant" in 2008 for her work in surmounting the limitations of earthbound telescopes. Early in her career, she developed a technique known as speckle imaging, which combined many short exposures from a telescope into one much-crisper image. Lately she's been using adaptive optics to further sharpen our view from here -- and compile evidence of young stars at the center of the universe.

"Few people know the center of the Milky Way -- some 26,000 light-years from Earth -- as intimately as Andrea Ghez." 

What is Speckle imaging ???? here is the answer !!!
 Speckle imaging (also known as video astronomy) describes a range of high-resolution astronomical imaging techniques based either on the shift-and-add ("image stacking") method or on speckle interferometry methods. These techniques can dramatically increase the resolution of ground-based telescopes.

Galactic collisions !!!!!!

Many galaxies are members of groups or clusters. Since groups and clusters contain so many galaxies relatively close together, it should not be surprising that galaxies sometimes collide with each other. In fact, the Milky Way Galaxy is colliding with the Sagittarius Dwarf Galaxy right now (see the SDSS First Discoveries for more information). Although galaxy collisions are common, stars in each galaxy are so far apart that collisions between stars are very rare.
Even if galaxies don't actually collide, though, they can still affect one another. When two galaxies pass close to one another, the force of gravity they exert on one another can cause both galaxies to bend out of shape. Both crashes and near misses between galaxies are referred to as "interactions."

At the right, you can see two galaxies interacting. You can see they are being distorted by the gravitational interaction between them. Can you imagine what they might have looked like before they interacted?
When two galaxies interact, clouds of gas inside each galaxy may become compressed. Compressing the clouds can cause them to collapse under their own gravity, turning into stars. This process can lead to a burst of star formation in interacting galaxies, leaving a new generation of stars in a galaxy where normal star formation may have ceased long ago.
Galaxy collisions take hundreds of millions of years, so we can't watch them happen. Instead, we use computer simulations to show us what would happen if two galaxies collided in a certain way. If you are interested in learning about galaxy collisions, you can use a web-based simulation tool to model them.

What Happens When Supermassive Black Holes Collide?

As galaxies merge together, you might be wondering what happens with the supermassive black holes that lurk at their centres. Just imagine the forces unleashed as two black holes with hundreds of millions of times the mass of the Sun come together. The answer will surprise you. Fortunately, it’s an event that we should be able to detect from here on Earth, if we know what we’re looking for.

Most, if not all, galaxies in the Universe seem to contain supermassive blackholes. Some of the biggest can contain hundreds of millions, or even billions of times the mass of our own Sun. And the environments around them can only be called “extreme”. Researchers think that many could be spinning at the maximum rates predicted by Einstein’s theories of relativity – a significant fraction of the speed of light.

As two galaxies merge, their supermassive black holes have to eventually interact. Either through a direct collision, or by spiraling inward until they eventually merge as well.

And that’s when things get interesting.

According to simulations made by G.A. Shields from the University of Texas, Austin, and E.W. Bonning, from Yale University, the result is often a powerful recoil. Instead of coming together nicely, the forces are so extreme that one black holes is kicked away at a tremendous velocity.

The maximum kick happens with the two black holes are spinning in opposite directions, but they’re on the same orbital plane – imagine two spinning tops coming together. In a fraction of a second, one black hole is given enough of a kick to send it right out of the newly merged galaxy, never to return.

As one black hole is given a kick, the other receives a tremendous amount of energy, injected into the disk of gas and dust surrounding it. The accretion disk will blaze with a soft X-ray flare that should last thousands of years.

So even though mergers between supermassive black holes are extremely rare events, the afterglow lasts long enough that we should be able to detect a large number out there in space right now. The researchers estimate that there could be as many as 100 of these recent recoil events happening within 5 billion light-years of the Earth.

Their recently updated journal article, entitled Powerful Flares from Recoiling Black Holes in Quasars will be published in an upcoming issue of the Astrophysics Journal.

Original Source: Arxiv