Myriad sparkling stars illuminate the billions of galaxies residing in the observable universe. The observable, or visible, Universe is the relatively small domain that we can observe of the unimaginably vast Cosmos. After the Big Bang, the light coming to us from farther areas has not had an adequate opportunity to reach us. This is attributable to the Space extension, and the uniform speed limit imposed by light. No observed pulse can move in a vacuum faster than light, but Space itself can, and therefore the very essence of our life will remain in Spacetime regions well beyond the limits of our sight.
The Cosmos galaxies are far away and mysterious, and the Sombrero Galaxy (Messier 104) stands out in the crowd as one of the most enchanting and disconcerting of its starlit kind. A team of astronomers revealed in February 2020 that data from the Hubble Space Telescope (HST) suggests that the multiple unusual and mysterious features of the Sombrero are the product of large galaxy mergers — though its smooth disk displays no indications of recent disastrous destruction. The Sombrero’s disk can, however, conceal the secret of a turbulent past.
The Sombrero has been a seductively tempting object for a long time because it seems to travel to the beat of a drum other than other known galaxies. This shows a mystifying combination of forms seen in disk-shaped spiral galaxies (like our own Milky Way), as well as elliptical galaxies in football form. With the new evidence from the HST, the tantalizing mystery of how it acquired its unusual structure becomes increasingly enthralling and bewildering.
The faint halo of the galaxy has some tattle-tale clues to it. It’s splattered with countless stars that are well-endowed by astronomers with heavier atomic elements — called metals. This is because they are icons of a later century. Using astronomers in terminology, a metal is an atomic element that is heavier than hydrogen and helium, and thus the same term has a different meaning for astronomers than it does for chemists. The Big Bang produced only lithium — hydrogen, helium, and traces — but the stars formed the rest.
The first generation of stars to dance in the Cosmos were the first to cook up the heavier atomic elements in their nuclear-fusing hearts — and then, when they went supernova, they sent them crying out into Space. Eventually, the freshly cast metals were introduced into subsequent generations of stars. The first stars (Population III) were born stripped of heavy metals since there were no stars to prepare them before them. The second generation of stars (Population II) is near, though not yet, stripped from metals because they are “polluted” with the batch that was formed in the first stars’ searing-hot cores. The youngest generation of stars (Population I)—of which our Sun is a member — contains the largest quantity of metals, having received these elements from earlier stars.
For this reason, stars with an abundance of heavy metals are generally only seen in the disk of a galaxy. As a result of ancient mergers with mature galaxies, which were heavily endowed with metals, the metal-rich stars of the Sombrero must have been thrown into their halo. Through its current “adulthood” the Sombrero world is more mature than it was in its “youth.” It is alone, too. This means that in the vicinity there is nothing else to eat. This observation puts a fresh perspective on the formation of galaxies in our Universe.
“The Sombrero has always been a bit of a peculiar galaxy, which makes it so fascinating. Hubble’s metallicity measures (i.e.: the concentration of heavy elements in the stars) are just another hint that the Sombrero has a lot to tell us about galaxy formation and development,” Dr. Paul Goudfrooij commented in a February 20, 2020, Hubblesite Press Release. Dr. Goudfrooij is from the Science Institute of the Space Telescope (STScI) in Baltimore, Maryland.
“Hubble ‘s observations of the Sombrero’s halo turn our accepted understanding of galaxy makeup and metallicity on its head,” co-investigator Dr. Roger Cohen, who is also from the STScI, added.
HST ‘s sensitivity has been able to overcome tens of thousands of single stars inhabiting the massive, stretched halo of the Sombrero. The halo is the area above the central portion of a galaxy and is usually comprised of older stars. These new Sombrero findings are surprising since they only reveal a tiny proportion of older, metal-poor stars in the halo, plus the excess of metal-rich stars in its disk and central bulge. Hence ancient, turbulent collisions with the galaxy and major mergers provide a possible explanation.
Strange And Beautiful
Owing to its unusual form and tremendous appeal, The Sombrero has captivated skywatchers for years. However, astronomers are now seeing the Sombrero in a different way, due to the latest findings from HSTs. The galaxy shows an extended halo brimming with metal-rich stars with scarcely any evidence of the predicted metal-poor stars in other galaxies’ halos. Astronomers, pouring over the HST data, have turned to sophisticated computer simulations to find a solution to this perplexing puzzle which poses a challenge to the conventional theory of galaxy formation.
Those results indicate the surprising possibility that major fusions occurred in the past of this strange galaxy, although the elegant and beautiful structure of the Sombrero shows no evidence of recent disruption. The implications of these recent observations were published in the Journal Astrophysique.
“The lack of metal-poor stars was a big surprise, and the abundance of metal-rich stars only added to the mystery,” Dr. Goudfrooij noted in the Hubblesite Press Release of 20 February 2020.
The Sombrero got its name because it resembles the broad rim and high-topped Mexican hat with this name — and it is seen almost edge-on, observed from Earth. This galaxy is also very bright, and small telescopes are easily observed with it. It’s only a bit above the height of the unassisted human eye, because of its light. The odd and magnificent galaxy sits on the southern edge of the densely inhabited Virgo System, and it is one of the galaxy’s most huge objects. Its density is essentially the size of 800 billion Suns. The Sombrero is stretching 50,000 light-years and centered 28 million light-years from Earth.
Often, the Sombrero contains a large community of globular clusters, which are strongly connected spherical star sets. It is estimated that almost 2000 globulars orbit this galaxy—10 times as many as our own barred-spiral Milky Way Galaxy orbits. The ages of the stars, though, are close to those around our Planet, varying from 10 to 13 billion years of age.
Inside the bright core of the Sombrero, a smaller disk is embedded and tilted relative to the large disk. X-ray emission indicates that material swirls down into the compact core of the galaxy, where a supermassive black hole dwells in sinister secrecy, waiting for its dinner to fall into its voracious maw. This supermassive black core comes in at 1 billion times the density of our Sun. The resident supermassive black hole in our Milky Way, by contrast, weighs “only” 4 million times the solar mass.
Some astronomers in the 19th century suggested that the Sombrero was just an edge-on disk of brightly shining luminous gas surrounding a youthful star — which is how our own Solar System evolved. In 1912, however, American astronomer V.M. Slipher (1875-1969) found the strange object seemingly flying away at 700 miles per second from Earth. That great velocity gave some of the earliest clues that the Sombrero was really another galaxy and that the Universe was expanding in every way.
Astronomers expect to find earlier generations of stars in the halo of a galaxy, with very small quantities of metals — compared to the more densely populated regions within the main disk of a galaxy. By the cycle of stellar nucleosynthesis, heavy atomic elements are formed, whereby stronger and heavy atomic elements are produced from lighter ones in the searing-hot heart of a star.
The longer a galaxy has to host heavy metal-creating stars, the more metal-rich its gas becomes — and the higher the metallicity of the stars born “polluted” from that gas. Such young, high-metallicity stars are typically found on a galaxy ‘s central disk since this is where a stronger stellar community resides.
However, in the Sombrero ‘s mysterious case things get complicated by the presence of a large number of globular clusters that contain elderly, metal-poor stars. These metal-poor, older stars are typically predicted to migrate past their host clusters and become part of the stellar halo. That process didn’t work in the Sombrero galaxy, however. The HST astronomers team compared their results with recent computer simulations to see what might be the origin of such a numerous population of metal-rich stars in the halo of this bizarre galaxy.
Their findings were shocking as they revealed that they generally well-ordered, healthy Sombrero had endured trillions of years earlier from aggressive accretion or significant merger incidents. In comparison, through the course of billions of years, our Milky Way is believed to have swallowed several tiny satellite galaxies in “minor” accretions. However, a major accretion event is very different because it involves the fusion of two or more similarly massive galaxies, both well-endowed with later-generation stars of higher metallicity.
The satellite galaxies produced only low-metallicity planets, consisting mainly of hydrogen and helium — the two lightest atomic elements — raised about 14 billion years ago in the Universe’s Big Bang conception (Big Bang nucleosynthesis). The heavy elements needed to be constructed by stellar nucleosynthesis in the searing-hot interiors of the stars and gradually integrated into subsequent stellar generations. In the case of small dwarf galaxies such as those surrounding our own Milky Way, this process was somewhat inefficient — while being considerably more effective in larger, more well-down galaxies such as ours.
The latest findings are shocking for the Sombrero galaxy as its flat, unperturbed disk displays no indications of a disturbance. For contrast, other communicating galaxies, such as the famous Antennae galaxies, derive their name from their spiral arms’ warped structure arising from the tidal powers of previous violent interactions. Mergers of equally huge galaxies typically coalesce with expanded halos into single large, smooth elliptical galaxies-a cycle that takes billions of years.
However, the Sombrero has always traveled to the beat of another drum, and it never fits the traditional definition of either a spiral or an elliptical galaxy altogether. Like nonconformist humans, it does what it wants. It’s a galactic mix of both.