Have you ever noticed a vacuum cleaner sucking in all the dust from your carpet? A black hole acts like a vacuum cleaner, sucking in the debris around it. But unlike a vacuum cleaner that uses suction power, a black hole uses the power of gravity -- which is so great that even light gets sucked in, making them invisible. And that is what makes them fascinating and a challenge to study!

What are black holes?

When a large star (such as our Sun) runs out of fuel, it can no longer hold its weight. The pressure from the layers of the star becomes so great that it collapses onto itself, creating a spectacular explosion. This is known as a supernova, and the dying star generates light that is a million times brighter than the galaxy itself! Once the explosion fades, a black hole is formed. As the star shrinks to the size of an atom, it retains the same mass. The resulting density (mass per unit volume) becomes so great that a black hole is formed.  

If black holes are invisible, how do scientists spot them? 

They do this by observing the black hole’s gravitational effects on stars and gases around it. As dust particles are pulled towards the black hole, they speed up and get hotter and hotter, and emit X-rays. Since X-rays do not enter the Earth’s atmosphere, scientists use satellites to detect sources of X-ray emission in space.

Most stars rotate around each other just like the planets in our solar system rotate around the Sun. If scientists are unable to see what the stars are rotating around, they suspect it is a black hole. There is yet another way scientists detect the presence of black holes.

How a black hole distorts image of a star -- known as gravitational lensing

Imagine you are an astronomer peering through a telescope at a star that is billions of miles away. You see a massive object (possibly a black hole) come in between the Earth and the star. You can still see the star – in fact, you can see two of the same stars and it seems brighter than usual! What's going on?

When a massive object comes between a star and the Earth, it acts like a lens and focuses the light from the star making it brighter. What about the duplicate stars? That is because lenses bend light rays and create duplicate images of the star. This is known as gravitational lensing. Still a little confused? Maybe the video [in the Notes] will help.

"Black Hole Hunter"

Meet NuSTAR -- Nuclear Spectroscopic Telescope Array, also referred to as ‘The Black Hole Hunter’. Launched recently by NASA from the Marshall Islands, the telescope will help astronomers better understand the size and power of black holes, and how they were formed. The telescope will map known black holes and hidden ones, as well as map explosions of supernovae and hunt for ancient supernovae remains.

Why is there so much hope for this telescope? Well, it is the first space-based telescope with direct imaging. It is 100 times more sensitive and has 10 times better resolution than previous telescopes. Also, it will be able to observe high energy x-rays emitted from black holes, nebulae and supernovas because of the specifically designed array of mirrors.

The NuSTAR telescope will open a new window to the universe and who knows -- we may see something unexpected!