Sagittarius A* (/ˈeɪ stɑːr/ AY star), abbreviated Sgr A* (/ˈsædʒ ˈeɪ stɑːr/ SAJ AY star), is the
Since the Milky Way contains over 100 billion stats, our home galaxy must harbor some 100 million black holes. Though detecting black holes is a difficult task and estimates from NASA suggest there could be as many as 10 million to a billion stellar black holes in the Milky Way.
But the Milky Way's black hole, Sagittarius A*, is actually much smaller than the first and was more difficult to see, since it required peering through the hazy disk of our galaxy.
Multiple NASA telescopes recently observed a massive black hole tearing apart an unlucky star that wandered too close. Located about 250 million light-years from Earth in the center of another galaxy, it was the fifth-closest example of a black hole destroying a star ever observed.
Astronomers have discovered the closest black hole to Earth, the first unambiguous detection of a dormant stellar-mass black hole in the Milky Way. Its close proximity to Earth, a mere 1,600 light-years away, offers an intriguing target of study to advance understanding of the evolution of binary systems.
For most space objects, we use light-years to describe their distance. A light-year is the distance light travels in one Earth year. One light-year is about 6 trillion miles (9 trillion km). That is a 6 with 12 zeros behind it!
Wormholes are a classic trope of science fiction in popular media, if only because they provide such a handy futuristic plot device to avoid the issue of violating relativity with faster-than-light travel. In reality, they are purely theoretical.
Problem is, no such thing has even been detected. Now part of the trouble is that these impacts would be rare. For the smallest PBH masses, there may only be one black hole hitting the earth every million years. For the Phobos-mass black holes or larger, you may only get one in the history of the earth.
For all practical purposes the matter has disappeared from the universe. Once inside the black hole's event horizon, matter will be torn apart into its smallest subatomic components and eventually be squeezed into the singularity.
As black holes evaporate, they get smaller and smaller and their event horizons get uncomfortably close to the central singularities. In the final moments of black holes' lives, the gravity becomes too strong, and the black holes become too small, for us to properly describe them with our current knowledge.
Is it possible for a black hole to "eat" an entire galaxy? No. There is no way a black hole would eat an entire galaxy. The gravitational reach of supermassive black holes contained in the middle of galaxies is large, but not nearly large enough for eating the whole galaxy.
So, if you had any plans to travel into a black hole, I urge you to reconsider. This isn't a way to quickly travel to another spot in the Universe, or transcend to a higher form of consciousness. There's nothing on the other side.
It is estimated that there are roughly 200 billion galaxies (2×1011) in the observable universe. Most galaxies are 1,000 to 100,000 parsecs in diameter (approximately 3,000 to 300,000 light years) and are separated by distances on the order of millions of parsecs (or megaparsecs).
Don't let the name fool you: a black hole is anything but empty space. Rather, it is a great amount of matter packed into a very small area - think of a star ten times more massive than the Sun squeezed into a sphere approximately the diameter of New York City.
In space or on the Moon there is no atmosphere to scatter light. The light from the sun travels a straight line without scattering and all the colors stay together. Looking toward the sun we thus see a brilliant white light while looking away we would see only the darkness of empty space.
Both galaxies are smaller and lower in mass than the Milky Way, but both house much more massive supermassive black holes than we do. In fact, of all of the spiral or elliptical galaxies known to host supermassive black holes, the Milky Way's is the least massive one known.
Near a black hole, the slowing of time is extreme. From the viewpoint of an observer outside the black hole, time stops. For example, an object falling into the hole would appear frozen in time at the edge of the hole.
Black holes are dark, dense regions in space where the pull of gravity is so strong that nothing can escape. Not even light can get out of these regions. That is why we cannot see black holes—they are invisible to our eyes. Because nothing can get out of black holes, physicists struggle understanding these objects.
At the center of a black hole the gravity is so strong that, according to general relativity, space-time becomes so extremely curved that ultimately the curvature becomes infinite. This results in space-time having a jagged edge, beyond which physics no longer exists -- the singularity.
Since nothing can escape from the gravitational force of a black hole, it was long thought that black holes are impossible to destroy. But we now know that black holes actually evaporate, slowly returning their energy to the Universe.
Nothing escapes a black hole. Any trip into a black hole would be one way. The gravity is too strong and you could not go back in space and time to return home. Aside from this, your body would be stretched and destroyed by the warping of space and the amount of radiation surrounding the event horizon.
Over timescales of 100 trillion years, it will fade away, eventually becoming a black dwarf. Any surviving planets in orbit around it must survive gravitational encounters in order to remain. If they can last long enough, eventually gravitational radiation will cause those worlds to be devoured by the stellar remnant.
Einstein's theory of general relativity mathematically predicts the existence of wormholes, but none have been discovered to date.
According to NASA, time travel is possible, just not in the way you might expect. Albert Einstein's theory of relativity says time and motion are relative to each other, and nothing can go faster than the speed of light, which is 186,000 miles per second. Time travel happens through what's called “time dilation.”
No one has yet seen a wormhole, but theoretically they could provide shortcuts to distant parts of the universe, or to other universes entirely, if they exist (SN: 7/27/17).