Finding A Galactic Treasure Where X Marks The Spot

A marvelous starlit pin-wheel whirling majestically in Space, our ancient barred spiral Milky Way Galaxy plays host to our Sun and its entire family of planets, moons, asteroids, and comets–as well as to billions of other stars beyond our own. Our Solar System inhabits the far suburbs of our Milky Way, in one of its spiral arms. However, our Galaxy is far from being alone–there are billions of galaxies in our visible Universe. The visible, or observable, Universe is that relatively small region of the entire Cosmos that we are able to observe. This is because the light streaming out from distant domains beyond our own cosmological horizon has not had sufficient time to reach us since the Big Bang birth of the Universe almost 14 billion years ago. Even though the Milky Way is our galactic home, it has nevertheless managed to keep some very well-hidden secrets–like buried treasures–from the prying eyes of curious astronomers who are trying to unveil its myriad mysteries. In July 2016, two astronomers–with the help of Twitter–announced that they have uncovered the strongest evidence to date that there is an enormous X-shaped structure composed of dazzling, fiery stars, tucked within the central bulge of our Galaxy.

Earlier studies that had used supercomputers, observations of galaxies other than our own, and studies of our own sometimes secretive Milky Way, whispered some very tantalizing hints of the real existence in Nature of that intriguing X-shaped structure. Alas, in the past, no one had succeeded in observing the mysterious X directly, and some astronomers began to suggest that this baffling X did not really exist.

“There was controversy about whether the X-shaped structure existed. But our paper gives a good view of the core of our own Galaxy. I think it has provided pretty good evidence for the existence of the X-shaped structure,” explained Dr. Dustin Lang in a July 19, 2016 University of Toronto Press Release. Dr. Lang, who is a co-author of the paper describing this discovery, is of the Dunlap Institute for Astronomy & Physics at the University of Toronto in Canada.

The results of this study appear in the July 2016 issue of the Astronomical Journal. The paper’s lead author is Dr. Melissa Ness, a postdoctoral researcher at the Max Planck Institute for Astronomy in Heidelberg, Germany.

Via Lactea

Our Milky Way Galaxy got its name because it appears as a gently glimmering and glowing, faint band that looks like a big celestial smile as it arches across our night sky. However, the separate stars within our Galaxy cannot be distinguished from one another by the naked eye as they swim around together in a distant sea of lovely light.

The “Milky Way” is a translation from the Latin via lactea, and the Greek “milky circle.” From our planet, our Galaxy appears to be a band across the night sky because we are seeing its disk-shaped structure from within. In 1610, Galileo Galilei was the first to resolve this gently glimmering band of distant light into its individual constituent stars with his primitive telescope–one of the first to be used for astronomical purposes.

Until the early 1920s, most astronomers thought that our Galaxy contained literally all of the stars in the Universe. In fact, they thought that our Milky Way really was the entire Universe! Eventually, observations conducted by the American astronomer Edwin Hubble revealed that our Milky Way is one of a multitude of galaxies in the visible Universe, now estimated to number 200 billion!

Our starlit barred-spiral Galaxy boasts an impressive diameter of approximately 100,000 to 120,000 light-years–but it very well may be as great as 150,000 to 180,000 light years. Astronomers usually estimate that our Milky Way hosts 100 to 400 billion stellar constituents, although it is entirely possible that the true number is about one trillion. It is also thought that there could be at least 100 billion planets circling stars in our Galaxy.

Our Solar System is situated in the Milky Way’s suburbs, within the Galactic disk that is located about 27,000 light years from its center on the inner edge of one of the spiral-shaped concentrations of gas and dust called the Orion Arm. The stars inhabiting the inner 10,000 light-years of our Galaxy form a bulge, as well as one or more bars that radiate outward from this bulge. The central heart of our Milky Way contains a powerful radio source which is likely a supermassive black hole that astronomers have named Sagittarius A* ( pronounced Sagittarius-A-Star). Our Galaxy’s resident supermassive black hole weighs millions of times more than our Sun, but it is a relative light weight, as far as supermassive black holes go. Supermassive black holes can be considerably more massive than Sagittarius A*, weighing as much as billions of times solar-mass. It is thought that most, if not all, of the large galaxies in the Cosmos host a supermassive black hole in their secretive hearts.

The stars and gases at a wide range of distances from the Galactic Center travel speedily on their orbits at approximately 220 kilometers per second. This constant speed of rotation contradicts the laws of Keplerian dynamics–suggesting that much of our Milky Way’s mass does not emit or absorb radiation, and as such is invisible. This transparent and invisible mass is termed dark matter, and there is much more of it than there is of the familiar atomic matter that we are used to. The so-called “ordinary” atomic matter accounts for literally all of the elements listed in the Periodic Table.

Our Universe is currently thought to be composed of approximately 71% dark energy, 24% dark matter, and a trifling 4.6% atomic (baryonic) matter. The mysterious dark energy accounts for the lion’s share of the Universe, causing it to accelerate in its expansion. The dark energy is most frequently believed to be a property of Spacetime itself.

The rotational period of our Galaxy is about 240 million years at the position of our Sun. Our Milky Way as a whole is traveling at a velocity of about 600 kilometers per second with respect to extragalactic frames of reference. The most elderly stellar population dwelling in our Galaxy is almost as old as the Universe itself, and these very old stars were born shortly after the cosmological Dark Ages that occurred soon after the Big Bang birth of the Universe almost 14 billion years ago.

Our Galaxy is accompanied by several small satellite galaxies, and it is a member of the Local Group of galaxies, which is itself a constituent of the Virgo Supercluster. Clusters and superclusters of galaxies are the largest structures known to inhabit the visible Universe, and they frequently play host to hundreds to thousands of individual galaxies that are all bound together by the force of their powerful mutual gravitational attraction. Our Milky Way’s Local Group contains more than 40 galaxies, of which our Galaxy and the Andromeda Galaxy are the largest members. The Andromeda Galaxy, like our own Milky Way, is a star-splattered, sparkling spiral whirling majestically in space.

In 2014 an international team of astronomers announced that they had succeeded in defining the contours of an almost unimaginably immense structure composed of galaxies, of which our Milky Way is a member. They named this enormous structure Laniakea, which is Hawaiian for “immense heaven”. Our Galaxy is situated in the outer limits of the Laniakea Supercluster, which is about 500 million light-years in diameter, and carries the amazing mass of 10 to the 17th power (a hundred quadrillion) blazing, brilliant stars that sparkle their way within 100,000 individual galaxies! The identity of the Great Attractor–an alluring mystery that has nagged at astronomers for the past thirty years–has been clarified by the discovery of the Laniakea Supercluster. Within the volume of the Laniakea Supercluster, movements are directed inwards–in a way that can be compared to the way streams of water move when they follow descending flows toward a valley down below. The Great Attractor region of the visible Universe is an enormous flat bottom gravitational valley with a sphere of attraction that extends all the way across the Laniakea Supercluster.

The sparkling starlit galaxies of our Universe trace out the mysterious and enormous web-like filaments of the Cosmic Web, composed of the mysterious dark matter–the identity of which remains unknown. However, scientists think that the dark matter is made up of unidentified, exotic, and non-atomic particles that do not interact with light, or any other form of electromagnetic radiation–which is why it is invisible. The starry galaxies that dance around together in immense groups and clusters light up this invisible Cosmic Web, illuminating that which otherwise could not be seen.

Our Galaxy can be observed as a hazy band of white light about 30 degrees wide arching across the night sky. When viewed from Earth, the visible region of the Milky Way’s Galactic plane occupies an area of the sky that includes 30 constellations. The center of our Galaxy is situated in the direction of the constellation Sagittarius–and it is here that the Milky Way is brightest. From Sagittarius, the hazy band of softly glowing white light appears to flow around to the Galactic anticenter in Auriga. The glimmering band then goes on the rest of the way around the sky, back to Sagittarius. The softly luminous band divides the night sky into two approximately equal hemispheres.

Our Milky Way Galaxy is the second-largest galactic constituent of the Local Group. with its stellar disk about 100,000 light-years in diameter, and on average approximately 1,000 light-years thick.This makes it somewhat less massive than the Andromeda Galaxy, which is also a spiral. A ring-like filament of sparkling stars, wrapping around our Galaxy, may really belong to the Milky Way itself, as it ripples both above and below the relatively flat Galactic plane. If so, it would indicate a mean diameter of 150,000 to 180,000 light-years.

Most of the Milky Way appears to be composed of the dark matter. Dark matter can only interact with “ordinary” atomic matter through the force of gravity. A halo composed of dark matter is spread out relatively uniformly, and this halo extends out to a distance beyond one hundred kiloparsecs from the Galactic Center.

Our Galaxy is composed of a bar-shaped core that is encircled by a disk of gas, dust, and billions of stars. The gas, dust, and fiery stars are organized in roughly logarithmic spiral arm structures. Astronomers first began to suspect that our Milky Way is a barred spiral galaxy, in contrast to an ordinary spiral galaxy, in the 1990s. Their suspicions were ultimately confirmed by observations made by NASA’s infrared Spitzer Space Telescope in 2005 that revealed our Galaxy’s central bar to be larger than previously thought.

Our Milky Way is far from being a simple structure, being made up of a duo of spiral arms, the bar-shaped feature that runs through its center, and its central bulge composed of stars. Our Milky Way’s bulge, like those possessed by other barred spiral galaxies, resembles a rectangular box or peanut when observed from within the plane of the Galaxy. The X-shaped structure is an integral component of the bulge.

X Marks The Spot

Astronomers think that our Galaxy’s bulge could have formed in two differing ways. It may have formed when our Milky Way merged with other galaxies, or it may have formed without the interference of others of its galactic kind as a result of the bar feature, which itself forms from the evolving galactic disk. Dr. Lang and Dr. Ness’s discovery supports the latter scenario which predicts the bow or peanut-shaped bulge and the Galactic X.

The most recent and clearest view of our Galaxy’s bulge emerged when Dr. Lang re-analyzed previously released data obtained from NASA’s infrared Wide-field Survey Explorer (WISE), a space telescope launched in 2009. Before completing its initial mission in 2011, WISE scanned the entire sky in infrared–imaging three-quarters of a billion galaxies, stars, and asteroids.

“The bulge is a key structure of formation of the Milky Way Galaxy. If we understand the bulge we will understand the key processes that have formed and shaped our Galaxy,” Dr. Ness explained in the July 19, 2016 University of Toronto Press Release.

“The shape of the bulge tells us about how it has formed. We see the X-shape and boxy morphology so clearly in the WISE image and this demonstrates that internal formation processes have been the ones driving the bulge formation,” she added.

In addition, it also can serve as evidence that our Milky Way did not undergo major merging events with other galaxies since the bulge formed. If it had, these disruptive interactions would have messed up its shape.

Dr. Lang’s analysis was originally intended to help in his research mapping the web of galaxies that dance around our visible Universe beyond our own Milky Way. In order to help explore the maps that he had constructed using the data derived from WISE, he developed an interactive map-browsing website–and then tweeted an image of the entire sky!

“Ness saw the tweet and immediately recognized the importance of the X-shaped structure. We arranged to meet at an upcoming conference we were both attending. The paper was born from that meeting. That’s the power of large surveys and open science,” Dr. Lang noted in the July 19, 2016 University of Toronto Press Release.

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