The Milky Way has an Inner Ring, Just Outside the Core

In the past century, astronomers have learned a great deal about the cosmos and our place in it. From discovering that the Universe is in a constant state of expansion to the discovery of the Cosmic Microwave Background (CMB) and the Big Bang cosmological model, our perception of the cosmos has expanded immensely. And yet, many of the most profound astronomical discoveries still occur within our cosmic backyard – the Milky Way Galaxy.

Compared to other galaxies, which astronomers can resolve with relative ease, the structure and size of the Milky Way have been the subject of ongoing discovery. The most recent comes from the Max Planck Institute for Extraterrestrial Physics (MPE), where scientists have found a previously undiscovered inner ring of metal-rich stars just outside the Galactic Bar. The existence of this ring has revealed new insights into star formation in this region of the galaxy during its early history.

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A Nearby Dwarf Galaxy has a Surprisingly Massive Black Hole in its Heart

Since the 1970s, scientists have known that within the cores of most massive galaxies in the Universe, there beats the heart of a Supermassive Black Hole (SMBH). The presence of these giant black holes causes these galaxies to be particularly energetic, to the point where their central regions outshine all the stars in their disks combined – aka. Active Galactic Nuclei (AGN). The Milky Way galaxy has its own SMBH, known as Sagitarrius A*, which has a mass of over 4 million Suns.

For decades, scientists have studied these objects in the hopes of learning more about their role in galactic formation and evolution. However, current research has shown that SMBHs may not be restricted to massive galaxies. In fact, a team of astronomers from the University of Texas at Austin’s McDonald Observatory recently discovered a massive black hole at the heart of a dwarf galaxy that orbits the Milky Way (Leo I). This finding could redefine our understanding of how black holes and galaxies evolve together.

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Those are Exoplanets. You’re Looking at Actual Exoplanets 63 Light-Years Away!

Located 63.4 light-years from Earth in the constellation Pictor is the young and bright blue star, Beta Pictoris. In 2008, observations conducted from the ESO’s Paranal Observatory in Chile confirmed the presence of an extrasolar planet. This planet was Beta Pictoris b, a Super-Jupiter with an orbital period of up between 6890 and 8890 days (~19 to 24 years) that was confirmed by directly imaging it as it passed behind the star.

In August of 2019, a second planet was detected (another Super-Jupiter) orbiting closer to Beta Pictoris. However, due to its proximity to its parent star, it could only be studied through indirect means (radial velocity measurements). After conducting a reanalysis of data obtained by the VLT, astronomers with the GRAVITY collaboration were able to confirm the existence of Beta Pictoris c through direct imaging.

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Galaxies Swell due to Explosive Action of New Stars

In 1926, famed astronomer Edwin Hubble developed his morphological classification scheme for galaxies. This method divided galaxies into three basic groups – Elliptical, Spiral and Lenticular – based on their shapes. Since then, astronomers have devoted considerable time and effort in an attempt to determine how galaxies have evolved over the course of billions of years to become these shapes.

One of th most widely-accepted theories is that galaxies changed by merging, where smaller clouds of stars – bound by mutual gravity – came together, altering the size and shape of a galaxy over time. However, a new study by an international team of researchers has revealed that galaxies could actually assumed their modern shapes through the formation of new stars within their centers.

The study, titled “Rotating Starburst Cores in Massive Galaxies at z = 2.5“, was recently published in the Astrophysical Journal Letters. Led by Ken-ichi Tadaki – a postdoctoral researcher with the Max Planck Institute for Extraterrestrial Physics and the National Astronomical Observatory of Japan (NAOJ) – the team conducted observations of distant galaxies in order to get a better understanding of galactic metamorphosis.

Evolution diagram of a galaxy. First the galaxy is dominated by the disk component (left) but active star formation occurs in the huge dust and gas cloud at the center of the galaxy (center). Then the galaxy is dominated by the stellar bulge and becomes an elliptical (or lenticular) galaxy. Credit: NAOJ

This involved using ground-based telescopes to study 25 galaxies that were at a distance of about 11 billion light-years from Earth. At this distance, the team was seeing what these galaxies looked like 11 billion years ago, or roughly 3 billion years after the Big Bang. This early epoch coincides with a period of peak galaxy formation in the Universe, when the foundations of most galaxies were being formed. As Dr. Tadaki indicated in a NAOJ press release:

“Massive elliptical galaxies are believed to be formed from collisions of disk galaxies. But, it is uncertain whether all the elliptical galaxies have experienced galaxy collision. There may be an alternative path.”

Capturing the faint light of these distant galaxies was no easy task and the team needed three ground-based telescopes to resolve them properly. They began by using the NAOJ’s 8.2-m Subaru Telescope in Hawaii to pick out the 25 galaxies in this epoch. Then they targeted them for observations with the NASA/ESA Hubble Space Telescope (HST) and the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile.

Whereas the HST captured light from stars to discern the shape of the galaxies (as they existed 11 billion years ago), the ALMA array observed submillimeter waves  emitted by the cold clouds of dust and gas – where new stars are being formed. By combining the two, they were able to complete a detailed picture of how these galaxies looked 11 billion years ago when their shapes were still evolving.

Observation images of a galaxy 11 billion light-years away. Credit: ALMA (ESO/NAOJ/NRAO), NASA/ESA Hubble Space Telescope, Tadaki et al.

What they found was rather telling. The HST images indicated that early galaxies were dominated by a disk component, as opposed to the central bulge feature we’ve come to associate with spiral and lenticular galaxies. Meanwhile, the ALMA images showed that there were massive reservoirs of gas and dust near the centers of these galaxies, which coincided with a very high rate of star formation.

To rule out alternate possibility that this intense star formation was being caused by mergers, the team also used data from the European Southern Observatory’s Very Large Telescope (VLT) – located at the Paranal Observatory in Chile – to confirm that there were no indications of massive galaxy collisions taking place at the time. As Dr. Tadaki explained:

“Here, we obtained firm evidence that dense galactic cores can be formed without galaxy collisions. They can also be formed by intense star formation in the heart of the galaxy.”

These findings could lead astronomers to rethink their current theories about galactic evolution and howthey came to adopt features like a central bulge and spiral arms. It could also lead to a rethink of our models regarding cosmic evolution, not to mention the history of own galaxy. Who knows? It might even cause astronomers to rethink what might happen in a few billion years, when the Milky Way is set to collide with the Andromeda Galaxy.

As always, the further we probe into the Universe, the more it reveals. With every revelation that does not fit our expectations, our hypotheses are forced to undergo revision.

Further Reading: ALMAAstrophysical Journal Letters

Rainbow Pictures Of Milky Way Show Off Galaxy’s Structure

Thanks to a new analysis of pictures obtained by a telescope in Chile, astronomers are gaining a better understanding of how the Milky Way formed and how our home galaxy has changed over the years.

Here’s how the project worked:

– The European Southern Observatory’s Visible and Infrared Survey Telescope for Astronomy (VISTA) 4.1-meter telescope took near-infrared pictures of the bulge of the Milky Way during the Variables in the Via Lactea public survey.

– Using the public data, scientists at the Max Planck Institute for Extraterrestrial Physics (MPE) created a three-dimensional star map of the inner regions of the Milky Way.

Milky Way. Image credit: NASA
Milky Way. Image credit: NASA

– Their findings were that the bulge in the center is shaped like a box or a peanut, with characteristics such as an “elongated bar”. It’s the first time such an accurate 3-D map of the inner universe was constructed, the science team said.

“This indicates that the Milky Way was originally a pure disk of stars, which then formed a thin bar, before buckling into the box/peanut shape seen today,” MPE stated. “The new map can be used for more detailed studies of the dynamics and evolution of our Milky Way.”

Among other conclusions, this helps confirm the fairly recent finding that the Milky Way is a barred spiral galaxy, rather than just a spiral galaxy.

More pictures and details are available at the Max Planck Institute for Extraterrestrial Physics’ website.