GALAXY

What is a galaxy?

We live on a planet called Earth that is part of our solar system. But where is our solar system? It’s a small part of the Milky Way Galaxy.

A galaxy is a huge collection of gas, dust, and billions of stars and their solar systems. A galaxy is held together by gravity. Our galaxy, the Milky Way, also has a supermassive black hole in the middle.

 

When you look up at stars in the night sky, you’re seeing other stars in the Milky Way. If it’s really dark, far away from lights from cities and houses, you can even see the dusty bands of the Milky Way stretch across the sky.

 

 

There are many galaxies besides ours, though. There are so many, we can’t even count them all yet! The Hubble Space Telescope looked at a small patch of space for 12 days and found 10,000 galaxies, of all sizes, shapes, and colors. Some scientists think there could be as many as one hundred billiongalaxies in the universe.

 

 Some galaxies are spiral-shaped like ours. They have curved arms that make it look like a pinwheel. Other galaxies are smooth and oval shaped. They’re called elliptical galaxies. And there are also galaxies that aren’t spirals or ovals. They have irregular shapes and look like blobs. The light that we see from each of these galaxies comes from the stars inside it.

Sometimes galaxies get too close and smash into each other. Our Milky Way galaxy will someday bump into Andromeda, our closest galactic neighbor. But don’t worry. It won’t happen for about five billion years. But even if it happened tomorrow, you might not notice. Galaxies are so big and spread out at the ends that even though galaxies bump into each other, the planets and solar systems often don’t get close to colliding.

The Tarantula Nebula

The Tarantula Nebula





This image of the dramatic star formation region 30 Doradus, also known as the Tarantula Nebula, was created from a mosaic of images taken using the HAWK-I instrument working without adaptive optics. 

Annotated wide-field view of the Tarantula Nebula (ground-based image)

 This wide-field view of the Tarantula Nebula was taken with the Wide Field Imager (WFI) on the MPG/ESO 2.2-metre telescope at the European Southern Observatory’s site at La Silla, Chile. This view shows the location of the heaviest star ever discovered (RMC 136a1, within the super star cluster RMC 136), the closest supernova to Earth to have been observed since the invention of the telescope (SN 1987a), plus the remnants of another supernova (NGC 2060). The Tarantula Nebula is the brightest nebula of its type in the local Universe.

 Merging clusters with the Tarantula

The main image shows the Tarantula Nebula from which a massive star (center of inset image) appears to have been ejected by even more massive siblings. The pictures were captured by the Wide Field and Planetary Camera 2 aboard the Hubble Space Telescope.
 

The Tarantula Nebula (NGC 2070, 30 Doradus) is the largest and brightest emission nebula in the Large Magellanic Cloud (LMC), 170,000 light-years away, and one of the largest emission nebulae known. The Tarantula Nebula lies at the eastern end of the LMC's stellar bar. It was first cataloged as a star, 30 Doradus, then discovered to be a nebula by Nicolas Lacaille in 1751–52.

 

Also known as the Looped Nebula (a name that goes back to John Herschel), the Tarantula is roughly 100 times larger than the famous Orion Nebula but is illuminated in the same way: by the ultraviolet radiation from a collection of hot, young, massive stars embedded within it. The Tarantula has been an active star-forming region for about the past 25 million years. Several OB associations have been observed inside it, including the extremely luminous and compact cluster R136 near its center; it is a hotbed of Wolf-Rayet stars. Supernova 1987A occurred in an outlying part of the Tarantula – a harbinger of what lies in store for many of the Nebula's stars.

 

Astronomers have observed a large number of massive young stars just outside the Tarantula Nebula that couldn't possibly have formed where they are, but almost certainly formed within the Tarantula and were then ejected at high speed because of gravitational interactions with other massive stars in the nebula.

 

While investigating these runaway stars using observations with the Hubble Space Telescope, a team of astronomers noticed something unusual about the R136 cluster at the heart of the nebula – it appears to be in the process of merging with a smaller cluster. Not only are the two clusters a different age, but the smaller one is elongated as if it is being stretched out of its originally spherical shape (see photo at right). This nearby example of cluster interaction should prove useful in understanding how star clusters may have formed in the early universe.





Tarantula