Category: Space Published: March 7, 2014
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The Top 50 Science Questions with Surprising Answers
Everything in the galaxy orbits the center of the combined mass of the entire galaxy and not the supermassive black hole that happens to be at the center. This image shows an artistic depiction of our galaxy. Public Domain Image, source: Christopher S. Baird.
Strictly speaking, everything in our galaxy does not orbit the supermassive black hole at the center. Everything in the galaxy orbits the center of mass of the galaxy. The supermassive black hole just happens to be at the center. If the black hole at the center were removed, the galactic orbits of almost all objects in the galaxy would not change (except for the few stars that are very close to the black hole). Our galaxy contains a lot of mass, which includes stars, gas, planets, and dark matter. The black hole in the center is only about one millionth of the total mass of our galaxy. Because mass causes gravity, and gravity causes orbits, the galactic orbital paths of all objects in the galaxy are caused by the total mass of the galaxy and not the mass of the black hole at the center.
Consider this analogy. Three girls form a circle and all lock their hands at the center of the circle. These girls now run quickly and steadily around their circle so that they can feel the strain in their arms. Even though they can feel the centrifugal force pushing them outwards, they do not fly off because their linked arms pull inward. The girls are all, in a sense, in orbit around their combined center of mass. They are not orbiting the gold ring on the finger of one of the girls, which happens to be at the center of their circle. If she took off her ring, their motion would not change much. The girls are like the objects in our galaxy, their linked arms are like the gravitational force linking everything together, and the gold ring is like the black hole. Every object in the galaxy is in orbit around the center of the combined mass of the galaxy. The center of mass is often called the "barycenter".
In general, small bodies do not orbit large bodies. Instead, large and small bodies together orbit their combined center of mass. The textbook "Orbital Mechanics" by Tom Logsdon notes, "Newton also modified Kepler's first law by noting that if both of the two bodies in question have appreciable mass, the smaller body will not orbit about the center of the larger body. Instead, both of them will orbit around their common barycenter. A similar phenomenon can be observed at a football game. When a majorette tosses her baton into the air, it does not rotate around the heavy end. Instead, the entire baton rotates about its center of mass."
Topics: barycenter, black hole, center of mass, galaxy, orbit
FAQs
The black hole in the center is only about one millionth of the total mass of our galaxy. Because mass causes gravity, and gravity causes orbits, the galactic orbital paths of all objects in the galaxy are caused by the total mass of the galaxy and not the mass of the black hole at the center.
Why does everything in our galaxy orbit the supermassive black hole in the center? ›
Gravitational Forces at Play
And when it comes to galactic orbits, the supermassive black hole is the main gravitational player. The gravitational pull of the supermassive black hole is immense, influencing the motion of stars and planets across the galaxy.
Why does every galaxy have a black hole at the center? ›
Their origin remains a mystery, however. They may have been created by the gravitational collapse of giant gas clouds from which galaxies were formed, or from the merger of many smaller black holes over time. Another possibility is that one simply grew over billions of years by steadily devouring orbiting stars.
What is black hole question answer? ›
A black hole is a place in space where gravity pulls so much that even light can not get out. The gravity is so strong because matter has been squeezed into a tiny space. This can happen when a star is dying. Because no light can get out, people can't see black holes.
What is the supermassive black hole at the center of the galaxy? ›
Sagitarrius A*, the supermassive black hole at the center of our galaxy, has been found to be spinning — and dragging space-time along with it.
Do galaxies orbit supermassive black hole? ›
No galaxy revolves around a supermassive black hole. True, some galaxies have supermassive black holes in their central regions. Like our Milky Way. And that black hole is big… about four million solar masses, give or take.
Does the sun orbit the black hole at the center of the galaxy? ›
Just like the moon orbits Earth and our planet orbits the sun, our home star is also circling the Milky Way — or, more accurately, orbiting the supermassive black hole at the center of our galaxy.
Can a black hole swallow a galaxy? ›
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.
What is at the center of the black hole? ›
Black holes have two parts. There is the event horizon, which you can think of as the surface, though it's simply the point where the gravity gets too strong for anything to escape. And then, at the center, is the singularity. That's the word we use to describe a point that is infinitely small and infinitely dense.
Where do black holes take you? ›
When matter falls into or comes closer than the event horizon of a black hole, it becomes isolated from the rest of space-time. It can never leave that region. For all practical purposes the matter has disappeared from the universe.
Black holes are a class of astronomical objects that have undergone gravitational collapse, leaving behind spheroidal regions of space from which nothing can escape, including light. Observational evidence indicates that almost every large galaxy has a supermassive black hole at its center.
Is there a black hole in the middle of each galaxy? ›
Not so rare. Most Milky Way-sized galaxies have monster black holes at their centers. Our is called Sagittarius A* (pronounced ey-star), and it's 4 million times the Sun's mass.
Do white holes exist? ›
White holes are the opposite of black holes, in that they spit out light and matter, rather than trapping it. So far, white holes are purely hypothetical objects, but astronomers are contemplating how they could form in reality.
Are many black holes located in the center of galaxies? ›
Supermassive black holes are a million to a billion times more massive than our Sun and are found in the centers of galaxies. Most galaxies, and maybe all of them, harbor such a black hole. So in our region of the Universe, there are some 100 billion supermassive black holes.
