Mrk 1216's Heavy Heart

Mrk 1216’s Heavy Heart

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According to the Standard Model of Cosmology, the total mass-energy of the Universe contains a mere 5% ordinary atomic matter and energy, 27% dark matter, and 68% dark energy. Dark energy is even more mysterious than the dark matter, and it is a substance that is causing the Universe to accelerate in its expansion. It has been proposed that the dark energy is a property of space itself. Dark matter accounts for 85% of total mass, while dark energy and dark matter account for 95% of the total mass-energy of the Cosmos. Hence, “most of the Universe is missing.” Ordinary atomic (baryonic) matter is clearly the runt of the universal litter of three, and it is really extraordinary material “Ordinary” atomic matter includes all of the elements listed in the familiar Periodic Table, and it composes the world that we are familiar with.

Since dark matter has not yet been observed directly, if it really does exist, it must barely dance with ordinary baryonic matter and radiation–except through the force of gravity.

Astronomers think that small galaxies (protogalaxies) were the first galactic structures to form in the ancient Cosmos. According to the bottom up theory of galactic formation, smaller protogalaxies emerged first, and then bumped into one another and merged–eventually growing into the immense and majestic galaxies that we observe today, such as our own barred spiral Milky Way. It has been proposed that the birthplace of a galaxy is within a transparent cradle composed of dark matter, termed a halo. In the primeval Universe, astronomers believe, the dark matter and baryonic matter danced together–clumping and, ultimately, weaving a complex web of intertwining, slender filaments. The great Cosmic Web of the Universe, as we see it today, is an enormous structure, composed of heavy filaments of dark matter, traced out by the visible starlight emitted by billions and billions of galaxies that are strung out along this large scale structure like glistening dewdrops on the web of an enormous spider.

According to the new study, conducted by the UCI astronomers, a halo–which can be described as a “fuzzy sphere”–composed of the mysterious dark matter, formed around the center of Mrk 1216 approximately 3 or 4 billion years after the Big Bang. This halo is thought to have extended over a larger area than the constituent stars within that galaxy. The formation of this type of red nugget galaxy was typical for many elliptical galaxies that dwell in our Cosmos today. However, in a way that differed from others of its kind, Mrk 1216 seems to have suffered from an atypical case of galactic arrested development. This is because most of the enormous elliptical galaxies continued to slowly grow larger and larger over cosmic time, when smaller galaxies collided and merged with them. However, little Mrk 1216 apparently traveled to the beat of a different drummer, and did not experience this more typical growth.

“The old ages and dense concentration of the stars in compact elliptical galaxies like Mrk 1216 seen relatively nearby provided the first key evidence that they are the descendants of red nuggets seen at great distances. We think the compact size of the dark matter halo seen here clinches the case,” noted study co-author Dr. Aaron Barth in the June 3, 2019 UCI Press Release. Dr. Barth is also of UCI.

Previously, astronomers calculated that the resident supermassive black hole that lurks hungrily in Mrk 1216 is more massive than expected for a galaxy of its relatively small mass. This more recent study, however, demonstrated that the black hole probably weighs-in at less than approximately 4 billion solar-masses. Even though this estimate indicates that Mrk’s 1216’s central black hole is quite hefty, it may really not be unusually massive for a galaxy as large as Mrk 1216.

The UCI scientists also went on the hunt for signs of outbursts emanating from Mrk 1216’s resident heavy dark heart. They observed tantalizing hints of cavities within the searing-hot gas akin to those seen in other massive galaxies and clusters of galaxies like Perseus. However, additional data are necessary in order to confirm their presence.

The Mrk 1216 data also provide important information about the nature of the mysterious and elusive dark matter. Because this invisible material has never been observed directly, some scientists are not convinced that it exists. In their study, Dr. Buole and Dr. Barth interpreted the Chandra data using both standard “Newtonian” models of gravity and a viable alternative theory called modified Newtonian dynamics (MOND). According to MOND, there is no need for dark matter in typical galaxies. However, the results of the new theory demonstrate that both theories of gravity need approximately the same immense quantity of dark matter to lurk in the heavy heart of Mrk 1216. Therefore, the two authors conclude that their study removes the need for the MOND interpretation.

Dr. Buole commented in the June 3, 2019 Chandra Press Release that “In the future we hope to go a step further and study the nature of dark matter. The dense accumulation of dark matter in the middle of Mrk 1216 may provide an interesting test for non-standard theories that predict less centrally concentrated dark matter, such as dark matter particles that interact with each other by an additional means other than gravity.”

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