The Milky Way: Out of an estimated 100 billion stars in our galaxy, no more than 14 may be made from antimatter. Antistars, which are identical to regular stars, save because they would burn antimatter at their cores. Antimatter is precisely like ordinary matter, but its charge is reversed. When antimatter and ordinary matter meet, they violently annihilate each other, leaving behind nothing but gamma rays.
Shortly after the Big Bang, nearly equal amounts of matter and antimatter were created. These twin materials crashed together into a spectacular spray of energy, leaving behind mainly matter built-in slightly higher proportions. Today, we are left with a matter-antimatter asymmetry problem, and we don’t know why.
The bulge and halo of the Milky Way (and other Sa and Sb galaxies) are composed mainly of old stars. This indicates that the bumps and halos of spiral galaxies probably formed through the primordial collapse of individual gas clouds early in the history of the Universe. Star formation is usually on the leading edge of the spiral arms where the cold gas of the thin disk is compressed and provides unequivocal evidence for ongoing secular evolution in thin disks.
An elliptical galaxy is a type of galaxy with an approximately ellipsoidal shape and a smooth, nearly featureless image. They are one of the three main classes of galaxies, along with spiral and lenticular galaxies.
There are 100,000,000,000 galaxies in the universe (best guess). Twenty percent of known galaxies are elliptical.
Lenticular galaxies generally have flat, disk-like shapes. However, unlike spiral galaxies, they lack the distinctive arms that usually wrap themselves around the central bulge. (Though, like both spiral and elliptical galaxies, they can have a bar structure passing through their cores.
Globular star cluster: An open cluster is a group of up to a few thousand stars formed from the same giant molecular cloud and are still loosely gravitationally bound to each other. In contrast, globular clusters are very tightly bound by gravity. Globular clusters are densely packed collections of ancient stars. Roughly spherical, they contain hundreds of thousands, and sometimes millions, of stars.
A Cepheid variable is a type of star that pulsates radially, varying in diameter and temperature and producing changes in brightness with a well-defined stable period and amplitude. This discovery allows one to know the actual luminosity of a Cepheid by simply observing its pulsation period. Cepheid Variables are very luminous stars, 500 to 300,000 times greater than the sun, with short periods of change that range from 1 to 100 days.
Local Group: Two massive bright spirals, the Milky Way and the Andromeda Galaxy dominate a gravitationally-bound group of around 40 galaxies known as the Local Group, which spans a volume of approximately 10 million light-years in diameter.
THE SOMBRERO GALAXY is one of the most extensive mosaics ever assembled from Hubble observations. The hallmark of the nearly edge-on galaxy is a brilliant, white, bulbous core encircled by thick dust lanes comprising the spiral structure of the galaxy. This island in the sky is one of the brightest galaxies in the universe. It is wound tight and super bright.
The Virgo Cluster: Is comprised of approximately 1300 (and possibly up to 2000) member galaxies. The cluster forms the heart of the larger Virgo Supercluster, of which the Local Group (containing our Milky Way galaxy) is a member.
The expansion of the universe is currently in overdrive. The space between galaxies is growing.
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