The Mystery Of The Galaxies That Shouldn’t Be There
By Judith E Braffman-Miller
Astronomers have wondered for decades how long it took for the islands of fiery, sparkling stars, that we call galaxies, to emerge out of the primeval darkness after the Big Bang birth of the Universe almost 14 billion years ago. In May 2017, a team of astronomers announced that they may have solved this nagging cosmic riddle when they discovered a new kind of galaxy haunting the ancient Universe less than a billion years after the Big Bang. These primordial galaxies are seen giving birth to new glittering baby stars more than a hundred times faster than our own Milky Way Galaxy does today. This important discovery could explain a mysterious earlier finding–that a population of surprisingly massive galaxies danced in the Cosmos only 1.6 billion years after its birth. The solution to this unsolved riddle requires the existence of some very fertile galactic precursors, capable of producing literally hundreds of billions of stars in a relatively brief period of time. The new observations also reveal what appears to be the most ancient image of galaxies in the process of merging together to form larger structures.
The results of this study, conducted by a team of astronomers led by Dr. Roberto Decarli of the Max Planck Institute for Astronomy (MPIA) in Germany, have been published in the May 28, 2017 issue of the journal Nature, under the title: Rapidly star-forming galaxies adjacent to quasars at z>6.
When a team of astronomers detected unusually massive galaxies, dwelling in the ancient Universe a few years ago, the puzzling size of these galaxies, containing hundreds of billions of stars, posed a delightfully intriguing puzzle for scientific detectives to solve. The galaxies are very far away, and we observe them now as they were only 1.5 billion years after the Universe was born in the Big Bang–when it was only about 10% its current age. How were these massive galaxies able to produce so many stellar babies, in such a comparatively brief time?
In astronomy, long ago is the same as far away. The more distant a shining object is in Space, the older it is in Time. A comparatively distant object’s traveling light takes a longer time to reach our telescopes because of the expansion of the Universe, and so we see these remote objects not as they are now, but as they were when they first sent forth their light to beam its shining way through Space–long ago and far away. No known signal can travel faster than light in a vacuum, and so the speed of light sets something of a universal speed limit.
The serendipitous discovery by the team of astronomers, led by Dr. Decarli, proposes a possible solution to this nagging mystery: a population of hyper-productive galaxies in the ancient Universe, existing at a time less than a billion years after the Big Bang.
“We were looking for something different: for star formation activity in the host galaxies of quasars. But what we found, in four separate cases, were neighboring galaxies that were forming stars at a furious pace, producing a hundred solar masses’ worth of new stars per year,” Dr. Decarli explained in a May 24, 2017 MPIA Press Release. Quasars constitute a brief stage of galactic evolution–they are exceptionally bright active galactic nuclei (AGN) powered by tumbling matter onto a voracious supermassive black hole hiding in the secretive heart of a galaxy. Supermassive black holes are thought to exist in the centers of perhaps every large galaxy in the observable Universe–including our own–and they weigh-in at millions to billions of times solar-mass. Our own Galaxy’s resident supermassive black hole, dubbed Sagittarius A (pronounced Sagittarius-A-Star) is a relative light-weight, as supermassive black holes go, weighing only millions–as opposed to billions–of times more than our Sun. It is a quiet old black hole now–dormant in its dotage–except for an occasional flare-up now and then, when it feasts on an unfortunate star, or a wandering cloud of ill-fated gas, as it once did during its glory days, when both it, and the Universe, were young. Many astronomers think that when our very ancient Milky Way Galaxy first formed billions of years ago, its resident Sagittarius A was a quasar, shooting out its shining beams of fiery light into the primeval Cosmos.
Our Milky Way is very similar to a vast number of other galaxies dispersed throughout the Cosmos. Its resident clouds of glowing gas and sparkling stars dwell within a disk that rotates around a central bulge where stars are situated much closer together, and where Sagittarius A* waits in sinister secret for its next banquet to tumble down into its maw. Our Star, the Sun, and its enchanting family of planets, moons, and assorted smaller objects is located approximately 25,000 light-years from the Galactic center. Light travels at about 5.88 trillion miles in one Earth-year.
From where we are situated, in the distant suburbs of our large barred-spiral Galaxy, the other stars appear to be concentrated in a glowing stripe across the sky–that magnificent stripe is our Milky Way. It is an impressive sight, and one that reveals to any observer on Earth that we are really only a very small part of that which is majestic, mighty, and vast beyond our wildest dreams. The stars that we can see within this band are orbiting around the Galactic center, taking more than 100 million Earth-years to finish a single orbit. The Andromeda Galaxy is our Milky Way’s nearest large galactic neighbor. Andromeda is also a spiral galaxy like our own.
Our Milky Way is an enormous disk, 100,000 light-years across. The most ancient stars inhabiting our Galaxy were born more than 10 billion years ago, long before our 4.56 billion-year-old Sun was born. The primordial soup that made up our Galaxy in its long-past youth was a comparatively simple recipe composed only of the lightest atomic elements. There was as yet no oxygen, carbon, nitrogen, oxygen, iron, or any other atomic element heavier than helium. Only hydrogen, helium, and traces of lithium and beryllium, were formed in the Big Bang fireball–all of the heavier atomic elements, called metals by astronomers, were manufactured in the searing-hot nuclear-fusing furnaces of the stars, or in the explosive supernova demise of massive stars. Supernovae form the heaviest atomic elements of all, such as gold and uranium.
Astronomers generally propose that small, amorphous galaxies, or protogalaxies, were the first galactic strcutures to be born in the primeval Universe. According to this bottom up theory of galactic formation, smaller protogalactic blobs formed first and then bumped into one another and merged in the ancient Universe–eventually growing larger and larger to evolve into the immense galaxies that we observe today. The cradle of a galaxy is termed the halo, and it is composed of a mysterious invisible substance termed dark matter. Even though the particles that compose the dark matter have not yet been identified, it is generally thought to be made up of non-atomic and exotic particles that do not interact with light or any other form of electromagnetic radiation. However, the invisible dark stuff–that is much more abundant throughout the Universe than atomic matter–reveals its strange, phantom-like presence by way of its gravitational influence on objects that can be observed–such as brilliant stars and wandering clouds of glowing gas. It is thought that in the primeval Cosmos, dark matter and the “ordinary” atomic matter that we are familiar with, did a bizarre dance together, spinning an immense and delicate web of intertwining filaments.
Galaxies come in three types: spirals, like our own Milky Way and Andromeda; ellipticals; and lenticular galaxies that look like a combination of the two others. Ellipticals are football-shaped galaxies that are immense, even when they are compared to large spirals. These gigantic galaxies host older, redder stars than spirals, that contain populations of younger stars. Also, in contrast to the elegant organization displayed by spirals–that look like enormous, lovely, starlit pin-wheels in Space–the stellar denizens of ellipticals wander around chaotically. It is generally thought that large elliptical galaxies are produced when two or more spirals collide and merge together to create one large elliptical galaxy, that is as large as the two disrupted spirals that are now combined into the structure of the newborn elliptical. The duo of supermassive black holes, haunting the hearts of both spirals, also merge. In this way, a supermassive black hole emerges that is as massive as the combined supermassive black holes of both former spirals.
However, the galaxies that inhabited the ancient Universe, were different–or so astronomers thought. Which brings us to the weird existence of galaxies that should not be there.
Fully Formed Mature Galaxies Not Long After The Big Bang
When astronomers observe our Milky Way Galaxy, with the telescopes available today, they can study both mid-sized and mature galaxies. When NASA’s Hubble Space Telescope (HST) was aimed at one small portion of the sky for 10 days, the image that resulted provided the most detailed window into the ancient Universe ever obtained. The HST image unveiled a bewitching, bothersome, and bewildering melange of many diverse galactic types: 1,500 galaxies at differing stages of evolution, with some dating back to the ancient era when the Universe was only a billion years old.
Within this HST Deep Field image are recognizable shapes: spherical ellipticals that sport a red hue because their light is emitted from mature stars, as well as a beautiful crystal blue spiral galaxy on fire with the newborn glow of young, searing-hot stars. There are also weird, “tadpole”-like objects, disrupted merging galaxies referred to as “train wrecks,” as well as a myriad of dim, “dwarf” galaxies. Some of the objects revealed in the image could date back to the very first generation of galaxies and stars to inhabit our baby Universe. Did these strange structures eventually evolve and grow into the majestic and recognizable galaxies observed in the Cosmos today? Are these shards and fragments really as small as the seem to be, but shining brightly as the result of great blasts of star-birth? Or, are these distant galaxies massive, with large portions of their stellar population hidden from the prying eyes of curious astronomers by impenetrable clouds of obscuring dust?
The categorization of galaxies into spirals, ellipticals, and lenticulars is termed the Hubble Sequence. Astronomers have wondered for years about how long it took after the Big Bang for these galaxies, filled with a treasure trove of stars, to form and then evolve into the mature structures observed today.
Dr. BoMee Lee, of the University of Maryland, concluded that the familiar spirals, ellipticals, and lenticulars existed at least as far back as 11.5 billion years ago. This means that the three types of galaxies formed “soon” (according to cosmological standards) after the Big Bang.
“The Hubble Sequence underpins a lot of what we know about how galaxies form and evolve; finding it to be in place this far back is a significant discovery,” Dr. Lee told the press in August 2013. Dr. Lee is the lead author in the study.
“This is the only comprehensive study to date of the visual appearance of the large massive galaxies that existed so far back in time. The galaxies look remarkably mature, which is not predicted by galaxy formation models to be the case that early on in the history of the Universe,” study co-author Dr. Arjen van der Wel noted in an August 2013 statement.
So, what do these distant large galaxies really look like? The team of astronomers say that they “appear to be split between blue star-forming galaxies with a complex structure–including disks, bulges, and messy clumps–and massive red galaxies that are no longer forming stars.”
A galaxy with the unexciting name of BX442 also should not be where it is. It is a spiral galaxy that inhabited the ancient Cosmos billions of years before most other spiral galaxies had sufficient time to form. In the July 19, 2012 issue of the journal Nature, a team of astronomers reported that they discovered this mysterious galaxy using the HST that was taking photographs of approximately 300 very distant galaxies inhabiting the ancient Universe. This very remote galaxy was discovered as it appeared only about 3 billion years after the Big Bang. The traveling light originating from this very distant galaxy has been wandering towards Earth for about 10.7 billion years. As astronomers peer back in Time to explore the primeval Universe, the most ancient galaxies usually look like train wrecks–clumpy, irregular, and not symmetric. However, BX442 is different–and it is beautiful.
This beautiful galaxy should not exist. It is what is termed a grand-design galaxy. This means that it has fully formed, prominent, pin-wheel-like spiral arms studded with stars. The problem is that grand-design galaxies should not inhabit the early Universe. In addition, BX442 is also relatively large when it is compared to the other galaxies that existed at this ancient time. This bizarre galaxy looks the way galaxies look today, but not the way galaxies looked long ago.
The Mystery Of The Galaxies That Shouldn’t Be There
Dr. Fabian Walter, leader of the observation program that detected hyper-productive galaxies in the early Universe, noted in the May 24, 2017 MPIA Press Release that “Very likely it is not a coincidence to find these productive galaxies close to bright quasars. Quasars are thought to form in regions of the Universe where the large-scale density of matter is much higher than average. Those same conditions should also be conducive to galaxies forming new stars at a greatly increased rate.” Dr. Walter and his team used the Atacama Large Millimeter-submillimeter Array (ALMA) observatory in Chile to make their discovery.
Whether or not these newly detected galaxies are really the ancient precursors of their more massive, later kin, thus solving the cosmic mystery, depends on how common they are in the Universe. This question may be answered by future follow-up observations planned by Dr. Decarli and his colleagues.
The ALMA observations also unveiled what appears to be the earliest known example of a duo of galaxies experiencing a merger. In addition to giving-birth to fiery baby stars, mergers are yet another important mechanism causing galactic growth. The new observations provide the first direct evidence that such mergers have been occurring even at the most ancient stages of galaxy evolution, less than a billion years after the Big Bang.
Judith E. Braffman-Miller is a writer and astronomer whose articles have been published since 1981 in various newspapers, magazines, and journals. Although she has written on a variety of topics, she particularly loves writing about astronomy because it gives her the opportunity to communicate to others the many wonders of her field. Her first book, “Wisps, Ashes, and Smoke,” will be published soon.