A galaxy is a system of stars, stellar remnants, interstellar gas, dust, and dark matter bound together by gravity
Largest known galaxy: IC 1101
The largest galaxy discovered to date is IC 1101. IC 1101 is classified as a supergiant elliptical galaxy, and it is very different from the Milky Way. As an elliptical galaxy, IC 1101 contains many red and yellow stars of low to intermediate mass, most of which are quite old. At the center of IC 1101 is a supermassive black hole, which turned out to be the largest black hole ever discovered. IC 1101 is estimated to be four million light-years in diameter. For comparison, the Milky Way is approximately 100,000 light years in diameter, making IC 1101 40 times larger than the Milky Way. If you were to place IC 1101 where the Milky Way is, it would completely engulf the Andromeda Galaxy 2, 5 million light years away. IC 1101 is about a billion light years from the Milky Way and probably contains over 100 trillion stars.
Hercules A
The elliptical galaxy, designated Hercules A, is the second largest known galaxy. Hercules A has an estimated diameter of 1, 5 million light-years, and like IC 1101, it is classified as a supergiant elliptical galaxy. Aside from the size and type of galaxy, not much is known about Hercules A, and for good reason. The supermassive black hole at the center of Hercules A is currently emitting two giant beams of radio waves. These beams are so energetic that they make it difficult to study the rest of the galaxy in detail. Even these beams of radio waves are huge, more than a million light-years long.
A2261-BCG
A2261-BCG is the third largest known galaxy in the Universe, with a diameter of one million light-years, about ten times the size of the Milky Way. A2261-BCG is a supergiant elliptical galaxy that is estimated to contain more than ten trillion stars. A2261-BCG is a rather strange galaxy for one simple fact: there is no supermassive black hole at its center. The vast majority of large galaxies in the Universe have a supermassive black hole at their center, but for unknown reasons, A2261-BCG does not. A2261-BCG is three billion light-years away.
ESO 306-17
The fourth largest known galaxy in the universe is ESO 306-17, with a diameter of approximately one million light-years. Like the galaxies discussed earlier, ESO 306-17 is a supergiant elliptical galaxy, but there is something that makes this particular galaxy unique. While most galaxies are in vast clusters of galaxies, ESO 306-17 is lonely and all the surrounding space is empty. Astronomers believe that ESO 306-17 may have once been one of many galaxies in its neighborhood, but it eventually merged with and absorbed every neighboring galaxy, causing it to grow in size and become one of the largest known galaxies in the universe. ESO 306-17 is about 500 million light-years away.
comet galaxy
The Comet Galaxy is the fifth largest known galaxy and the first galaxy on the list that is not an elliptical galaxy. The Comet Galaxy is a spiral galaxy 600,000 light-years in diameter. The Comet galaxy is also one of the fastest galaxies in the universe, moving at two million miles per hour (3, 22 million kilometers per hour). As this galaxy rushes through space, it is literally being torn apart by the gravitational force of other nearby galaxies. These gravitational forces, combined with the speed of the galaxy, cause a huge tail of material to form, making it look like a comet. The Comet galaxy is 3, 2 billion light years away from us.
The Condor Galaxy
The Condor Galaxy is the sixth largest known galaxy in the Universe with a diameter of 522,000 light-years. The Condor Galaxy is a large spiral galaxy with two outward protruding arms. Interestingly, astronomers believe that the reason for the highly elongated spiral arms in the Condor galaxy is due to a brief collision with another neighboring galaxy many millions of years ago. The Condor galaxy is 212 million light years away from us.
UGC 2885
The seventh largest known galaxy is UGC 2885, with a diameter of 463,000 light-years. Unlike the first four galaxies considered, UGC 2885 is a spiral galaxy very similar to our Milky Way. Interestingly, UGC 2885 exists in a rather empty region of space, and there are no other galaxies in the vicinity of UGC 2885. Unlike ESO 306-17, which grew to a huge size by swallowing all the neighboring galaxies, grew from the accretion of huge amounts of hydrogen. UGC 2885 is 232 million light years away from us.
ESO 444-46
ESO 444-46 is the eighth largest known galaxy in the Universe, with a diameter of 400,000 light-years. ESO 444-46 is classified as a supergiant elliptical galaxy, and is believed to have grown to its current size through the merger and absorption of many other galaxies. ESO 444-46 is home to one of the largest populations of star clusters in the Universe, numbering about 27,000 of them. ESO 444-46 is about 640 million light-years away.
Galaxy Tadpole
The Tadpole Galaxy is the ninth largest known galaxy with a diameter of 280,000 light-years. Like the Milky Way, the Tadpole Galaxy is a spiral galaxy, but it has one unique feature that sets it apart from most galaxies. The Tadpole Galaxy is followed by a vast chain of stars that extends outward from the galaxy, forming something that looks like a tadpole's tail. It is this tail that makes the Tadpole Galaxy so huge, as it stretches out over many thousands of light-years. Astronomers believe that this vast trail of stars formed after a nearby galaxy approached the Tadpole galaxy in the distant past. The other galaxy's gravitational pull would have shattered the shape of the Tadpole Galaxy, pulling stars outward in the process. The Tadpole Galaxy is 420 million light years away.
Andromeda Galaxy
The title of the tenth largest galaxy in the Universe belongs to our nearest galactic neighbor, the Andromeda Galaxy. And Andromeda is about twice the size of the Milky Way, having a diameter of about 200,000 light years. Much of what we know about our own galaxy is actually derived from observations of Andromeda, since the two galaxies are very similar. Andromeda is a spiral galaxy, very similar in shape to the Milky Way. One day, in about ten billion years, the Milky Way and Andromeda will probably merge together and eventually form one much larger galaxy. Andromeda is the closest galaxy to the Milky Way, 2, 5 million light-years away.
