We still do not know exactly what its structure is. It absorbs even the light around it due to its incredible gravitation. It, even considered as a door to an alternative universe according to some theories among thousands of different theories of scientists, is the topic for this issue. What do you think it is?

The second issue of our Astro Newsletter, feeding space enthusiasts with science, is ready to reveal the unknown about the most asked topic about space.

Black Holes

Let's go on a journey into the unknown and illuminate the darkest spots of the universe together.

Since it does not contain even a light inside or around it, this unknown place is called a "black hole". The name was first used in 1967 by theoretical physicist John Wheeler in a conference at NASA.

How do we see black holes that don't even have light?

The importance of the light in observation of the universe is enormous. In simple observation telescopes that we use to observe space from Earth, an image is obtained as a result of magnifying the light of the celestial body in space with the help of a lens. In such a case, it will be impossible to observe a black hole which does not have even light by using observation telescopes.

However, if there is a star or high-density gas component near the black hole, the black hole can pull them right into itself.

Those pulled materials form a structure called accretion disk around the black hole. This structure creates a spiral structure just like a sink drain towards the inside of the black hole, and the objects following this structure are swallowed by the black hole. The accretion disk orbits around the black hole at almost the speed of light, and the temperature rises to millions of degrees due to the collision or friction of the particles in the disk. At this stage, a black hole can be mentioned when this temperature is detected by advanced telescopes that make X-ray observations.

harvard.edu

The supermassive black hole in the center of gigantic elliptical galaxy M87 was observed with this method for the first time in April 2019 as part of the Event Horizon Telescope project.


wikimedia.org

There are three different types of black holes, which we can classify as larger or smaller like every other object in the universe.  

Stellar-Mass Black Holes

They are also called remnants of massive stars. The diameters of these black holes are typically between 16 and 48 km. Depending on the mass of the star, this type of black hole is formed when a star much larger than the Sun explodes and collapses with a supernova. If the mass of the star is relatively low, a star called Neutron may form instead of a black hole when this collapse stops at one point. The proportion of these black holes in the observable universe is about 1%. Although this percentage may seem small, scientists think that there are more than 40 Centrillion (40x1018) stellar-mass black holes in the observable universe.


nasa.gov

Intermediate Black Holes

These are slightly larger than stellar-mass black holes and way smaller than supermassive black holes were introduced in 2021. It was first discovered by scientists following a gamma-ray burst. These black holes are also formed as a result of collapse of the star but this time the star is way bigger. The mass of the first discovered mid-level black hole is 55 thousand times greater than the Sun.

nasa.gov

Supermassive Black Holes

The biggest, most surprising, and most intriguing black holes are supermassive black holes. The mass of these black holes is billions of times greater than the Sun. According to a general theory, there is one of these black holes at the center of each galaxy. For example, Sagittarius A, believed to be located in the center of our own galaxy (Milky Way), has a mass of about 4 million times greater than the mass of the Sun.

Researches continue on how supermassive black holes form. As a result of these studies, the most supported theory is that supermassive black holes may have formed from collapsing interstellar hydrogen clouds in the early history of the universe. According to another theory, these black holes were formed as a result of the merging of more than one black hole and accumulating excess mass over the centuries.


nasa.gov

So what is inside a black hole?

Unfortunately, we cannot see inside black holes where even light is trapped. However, according to astrophysical theories, the center of a black hole is also known as the place where the mass of the entire black hole is concentrated in a small point of infinite density (singularity). This point is thought of as the center of that enormous gravitational force of the black hole. We can only understand the gravitational force here with quantum physics. However, since we do not yet have a quantum theory of gravity, it is unfortunately impossible to define what actually happens at the center of a black hole.

Thanks to the developing technology, we photographed a black hole for the first time using eight different telescopes from all over the world. Also, we are building Quantum computers by developing technological systems, trying to make calculations with those computers and trying to reveal the secrets of the universe day by day.

Do you think the secrets of black holes will be solved in the near future? Will Einstein’s and Hawking's theories be proven?

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