One says that galaxies were born when vast clouds of gas and dust collapsed under their own gravitational pull, allowing stars to form. The other, which has gained strength in recent years, says the young universe contained many small "lumps" of matter, which clumped together to form galaxies.
Explanation:
The process repeats: Gravity condenses gas into galaxies and stars, stars blow up and kick the gas out, gravity cycles the gas back in and makes new stars. ... Without gas, it can't form new stars; the old stars live out their lives and die, and eventually the galaxy dies too.
One says that galaxies were born when vast clouds of gas and dust collapsed under their own gravitational pull, allowing stars to form.
The other, which has gained strength in recent years, says the young universe contained many small "lumps" of matter, which clumped together to form galaxies. Hubble Space Telescope has photographed many such lumps, which may be the precursors to modern galaxies. According to this theory, most of the early large galaxies were spirals. But over time, many spirals merged to form ellipticals.
The galaxy-formation process has not stopped. Our universe continues to evolve. Small galaxies are frequently gobbled up by larger ones. The Milky Way may contain the remains of several smaller galaxies that it has swallowed during its long lifetime. The Milky Way is digesting at least two small galaxies even now, and may pull in others over the next few billion years.
Galaxy mergers happen fairly often. A large portion of the bright galaxies that we see today may have formed from the mergers of two or more smaller galaxies.
Mergers are common because the universe is crowded on the galactic distance scale. The disk of the Milky Way, for example, spans about 100,000 light-years; the nearest major galaxy, the great spiral in Andromeda, which is a little bigger than the Milky Way, is about 2.5 million light-years away. That means the distance between these two galaxies is only about 25 times greater than the sizes of the galaxies themselves. That doesn't leave a lot of "elbow room" for galaxies.
Answers & Comments
Answer:
One says that galaxies were born when vast clouds of gas and dust collapsed under their own gravitational pull, allowing stars to form. The other, which has gained strength in recent years, says the young universe contained many small "lumps" of matter, which clumped together to form galaxies.
Explanation:
The process repeats: Gravity condenses gas into galaxies and stars, stars blow up and kick the gas out, gravity cycles the gas back in and makes new stars. ... Without gas, it can't form new stars; the old stars live out their lives and die, and eventually the galaxy dies too.
Answer:
One says that galaxies were born when vast clouds of gas and dust collapsed under their own gravitational pull, allowing stars to form.
The other, which has gained strength in recent years, says the young universe contained many small "lumps" of matter, which clumped together to form galaxies. Hubble Space Telescope has photographed many such lumps, which may be the precursors to modern galaxies. According to this theory, most of the early large galaxies were spirals. But over time, many spirals merged to form ellipticals.
The galaxy-formation process has not stopped. Our universe continues to evolve. Small galaxies are frequently gobbled up by larger ones. The Milky Way may contain the remains of several smaller galaxies that it has swallowed during its long lifetime. The Milky Way is digesting at least two small galaxies even now, and may pull in others over the next few billion years.
Galaxy mergers happen fairly often. A large portion of the bright galaxies that we see today may have formed from the mergers of two or more smaller galaxies.
Mergers are common because the universe is crowded on the galactic distance scale. The disk of the Milky Way, for example, spans about 100,000 light-years; the nearest major galaxy, the great spiral in Andromeda, which is a little bigger than the Milky Way, is about 2.5 million light-years away. That means the distance between these two galaxies is only about 25 times greater than the sizes of the galaxies themselves. That doesn't leave a lot of "elbow room" for galaxies.