A vast multitude of incandescent stars emit their lovely glittering light within the more than 100 billion galaxies that float around in the observable Universe. The observable, or visible, Universe is that region of our Cosmos that we are able to see, both with our unaided eyes and with some very sophisticated telescopes. We cannot observe what may (or may not) exist beyond the edge (the horizon) of our observable, or visible, Universe. This is because the light of whatever may exist beyond the cosmological horizon has not had enough time to reach us since our Universe was born in the Big Bang almost 14 billion years ago.
Our own large barred spiral Galaxy, the Milky Way, is much like a very large number of other galaxies dispersed throughout our Universe. Its constituent stars and gas reside primarily in a disk, rotating around a central bulge where stars reside much closer together, and where there also lurks a supermassive black hole. Supermassive black holes weigh as much as millions to billions of times more than the Sun. The supermassive black hole believed to reside at the center of our Milky Way is a relative light-weight. It weighs “only” millions, rather than billions, of solar-masses. The Sun, and its enchanting retinue of familiar planets, moons, and assorted smaller objects is located about 25,000 light-years from the Galactic center, where the black hole dwells. Light travels about 9.46 trillion kilometers or 5.88 trillion miles in one Earth-year.
From where we are situated, in the far suburbs of our Galaxy in one of its spiral arms, the other stars appear to be concentrated in a stripe across the sky–that stripe is the Milky Way. Because of light pollution on our planet, many of its inhabitants have never had the opportunity to see the band of stars in the night sky that compose our Galaxy. For those of us who have seen this awesome band, it is an impressive sight, and one that truly drives home to any observer on Earth that we are just an exquisitely tiny component of that which is immense, majestic, and mighty. The stars that we see in this band are circling around the Galactic center, taking over 100 million Earth-years to complete a single orbit. The Andromeda Galaxy is our Galaxy’s nearest large neighbor in space. It is a spiral galaxy like our own Milky Way, but it is a larger spiral, and it hosts a larger supermassive black hole in its heart.
The Andromeda Galaxy is 2 million light-years away–at present. Like our own Galaxy, it contains stars of all ages and a rich supply of gas. Gravity is drawing Andromeda towards us at approximately 100 kilometers a second. In about 5 billion years, our Galaxy will collide and merge with Andromeda.
Our large Galaxy, the Milky Way, and the even larger spiral, Andromeda, together with at least 20 smaller galaxies, constitute what is called the Local Group. The Local Group is a few million light-years across. However, this is small when compared to entire galaxy clusters. Immense clusters of galaxies exist in our Universe, and some of them contain hundreds of constituent galaxies. Our Local Group is situated near the outer limits of the Virgo Cluster of galaxies, whose core is 50 million light-years away from us. The many groups of galaxies and clusters of galaxies are themselves smaller constituents of gigantic web-like filaments and wide, thin expanses. The so-called Great Wall of galaxies is, for example, a sheet-like collection of galaxies situated about 200 million light-years away from us, and a similar enormous structure is termed the Great Attractor. The Great Attractor is pulling relentlessly, with its mighty gravitational grip, on the entire Virgo Cluster of galaxies. We go along for the ride, of course, together with the rest of the Local Group, at approximately several hundred kilometers per second.
As we probe deeper and deeper into ever-more-remote regions of Space with increasingly improved telescopes, both Space-borne and Earth-bound, we see larger numbers of more distant galaxies, more and more clusters similar to Virgo, and more and more gigantic sheet-like and filamentary structures like the Great Attractor and the Great Wall. But if we observe the galaxies from a cosmological perpective, the galaxies themselves are just beautiful beads of light dispersed throughout the Universe. These luminous beads of light outline for us how the contents of the Universe are distributed. The immense filaments and sheets that those lovely beads of light illuminate–and are strung out along like dewdrops on the web of some gigantic spider–are composed of exotic and bizarre material known as dark matter. Dark matter is not composed of ordinary atomic material of which stars, planets and people are made. Dark matter is composed of some as yet unidentified exotic particle that does not interact with light and is, therefore, invisible. However, we do strongly suspect that it is there because it interacts with ordinary atomic matter by way of gravitation. Therefore, we can observe the gravitational effects of dark matter on the ordinary matter that we can see, such as brilliantly starlit galaxies.
The Milky Way is an enormous disk, 100,000 light-years across. It contains a hundred million stars. The most ancient stars in the Milky Way formed more than 10 billion years ago, long before our middle-aged Sun was born about 4.56 billion years ago. The primordial brew that composed our Galaxy during its youth was a comparatively uncomplicated soup of only the simplest atoms. There was no carbon, oxygen, or iron. In our Galaxy’s early youth, chemistry was very simple. Before more complicated chemical compounds could emerge, and before a Solar System such as ours could appear, ancient stars had to transmute, recombine, and re-use the chemical elements. The chemically exciting atoms, those that were the precursors to complexity and life in our Solar System, were initially forged inside the first generation of ancient stars dwelling in our Galaxy more than 10 billion years ago. A carbon atom that had been built up from the fusion of helium atoms inside an ancient star that ultimately blew itself to pieces in a gigantic supernova blast in the remote past–sending the carbon atom screaming into Space–might have taken an aimless journey between the stars for hundreds of millions of years before it found itself residing in a frigidly cold and dense knot, inside a dark, interstellar molecular cloud, which ultimately collapsed under its own gravity to give birth to a new baby star. For billions of years, stars have decorated the unimaginably enormous number of galaxies in our Universe with their beautiful glittering light.
It is generally thought that small galaxies, or protogalaxies, were the first galactic structures to form in the Universe. According to this “bottom up” theory of galactic formation, smaller protogalaxies formed first and then collided and merged together in the ancient Cosmos, to eventually form the majestic, enormous galaxies that we see today. The birthplace of a galaxy is in a cradle of invisible dark matter, termed a halo. In the very ancient Universe, it is believed, that dark matter and “normal” atomic matter clumped together, forming a web of slender, intertwining filaments.
The galaxies that we see today in the Universe divide into specific types, including spiral galaxies like our own Milky Way and the neighboring Andromeda, which contain stars of all ages. Elliptical, or football-shaped galaxies, are enormous even when compared with spirals, and they contain mostly older, redder stars traveling around chaotically Ellipticals often form after the collision and merger of two or more spiral galaxies. In about 5 billion years, when the Milky Way and Andromeda collide and merge, they will form a large elliptical galaxy that is twice as large as the two former spirals. The supermassive black holes of both galaxies will also merge, creating an even more massive solitary supermassive black hole in the new elliptical galaxy’s center.
The galaxies that dwelled in the early Universe, however, were different–or so astronomers thought. The early galaxies showed much greater diversity, and there was a much larger population of irregular galaxies. Irregulars are usually small galaxies of low mass, and with no specific form–such as the beautiful pinwheel shape of spirals and the football shape of ellipticals.
Which brings us to the bizarre existence of a galaxy that should not be there. The galaxy, with the unglamorous name of BX442, is truly an enigma wrapped in mystery. It is a spiral galaxy that dwelled in the early Universe billions of years before most other spiral galaxies had the time to form. In a study reported in the July 19, 2012 issue of the journal Nature, astronomers said they discovered the strange structure while using the venerable Hubble Space Telescope to take photographs of around 300 extremely remote galaxies dwelling in the early Universe. This very remote spiral galaxy was discovered as it existed only about three billion years after the Big Bang birth of our Universe. The light from this remote region of the observable Universe has been wandering to our planet for roughly 10.7 billion years. Dr. Alice Shapley, an associate professor of physics and astronomy at UCLA, and co-author of the study, commented in the July 18, 2012 e! Science News: “As you go back in time to the early Universe, galaxies look really strange, clumpy and irregular, not symmetric. The vast majority of old galaxies look like train wrecks. Our first thought was, why is this one so different, and so beautiful?”
This lovely galaxy should not exist. It is a so-called grand-design galaxy, indicating that it has well-formed, prominent spiral arms–and grand-design galaxies were thought not to exist at such early times in the history of the Universe. BX442 is also relatively large when compared to other galaxies that dwelled in the early Universe–only about 30 of the galaxies observed in this study, whose lead author is Dr. David Law, a Dunlap Institute postdoctoral fellow at the University of Toronto’s Dunlap Institute for Astronomy and Astrophysics, are as massive as this strange spiral.
Why does this mysterious galaxy look the way galaxies look today, but not the way galaxies looked in early times?
Study co-authors, Drs. Law and Shapley, think the answer may lie in the existence of a nearby, companion dwarf galaxy, and the gravitational interaction between the two galaxies. Support for this theory is suggested by a numerical simulation conducted by Dr. Charlotte Christensen, a postdoctoral scholar at the University of Arizona, and a co-author of the Nature paper. Eventually, the dwarf galaxy is likely to collide and merge with BX442.
Galaxies dwelling in the early Universe were much more likely to collide and merge together than galaxies of today’s Universe. Gas pouring down from intergalactic space fed stars that were forming at a much more rapid rate as well. The Universe today is rather dull in comparison to the way it was in early times.
As Dr. Shapley noted in the same issue of e! Science News: “We first thought this could just be an illusion, and that perhaps we were being led astray by the picture. What we found (was) that the spiral arms do belong to this galaxy. It wasn’t an illusion. We were blown away.”
