How Do Stars Get Kicked Out of Globular Clusters?

Hubble image of Messier 54, a globular cluster located in the Sagittarius Dwarf Galaxy. Credit: ESA/Hubble & NASA

Globular clusters are densely-packed collections of stars bound together gravitationally in roughly-shaped spheres. They contain hundreds of thousands of stars. Some might contain millions of stars.

Sometimes globular clusters (GCs) kick stars out of their gravitational group. How does that work?

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A Dwarf Galaxy Passed Close to the Milky Way and Left Ripples in its Wake

Artist's view of ripples on the edge of the Milky Way. Credit: NASA JPL-Caltech R. Hurt (SSC Caltech)

When you imagine the collision of galaxies, you probably think of something violent and transformational. Spiral arms ripped apart, stars colliding, cats and dogs living together, mass hysteria. The reality is much less dramatic. As a recent study shows, our galaxy is in a collision right now.

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Thanks to Gaia we Know Exactly how and When the Sun Will die

How different types of stars live and die. Credit: ESA

Our Sun is doomed. Billions of years from now, the Sun will deplete its hydrogen fuel and swell to a red giant before becoming a white dwarf. It’s a well-known story, and one astronomers have understood for decades. Now, thanks to the latest data from Gaia, we know the Sun’s future in much greater detail.

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Recent Supernovae Produced Giant Cavities in the Orion Nebula

This image of the Orion Nebula shows the puzzilng Barnard's Loop feature, a structure made of gas first identified in 1898, Image Credit: Michael Foley

The Orion Nebula is a well-known feature in the night sky and is visible in small backyard telescopes. Orion is a busy place. The region is known for active star formation and other phenomena. It’s one of the most scrutinized features in the sky, and astronomers have observed all kinds of activity there: planets forming in protoplanetary disks, stars beginning their lives of fusion inside collapsing molecular clouds, and the photoevaporative power of massive hot stars as they carve out openings in clouds of interstellar gas.

But supernova explosions are leaving their mark on the Orion Nebula too. New research says supernovae explosions in recent astronomical history are responsible for a mysterious feature first formally identified in the night sky at the end of the 19th century. It’s called Barnard’s Loop, and it’s a gigantic loop of hot gas as large as 300 light-years across.

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The Milky Way’s Most Recent Meal was a Galaxy it Gobbled up 8-10 Billion Years ago

Gaia-Enceladus in a simulation of a galactic merger with the Milky Way matching Gaia data. Credit: ESA (artist’s impression and composition); Koppelman, Villalobos and Helmi (simulation)

A central aspect of galactic evolution is that they must eat or be eaten. Dark energy strives to push galaxies apart, but gravity tries to pull them together. As a result, galaxies tend to form into local groups. As these superclusters of galaxies become more isolated due to cosmic expansion, they gravitationally turn on each other, and in time the largest galaxies of the group will consume the smaller ones. The Milky Way is one of the larger galaxies in our local group, and so it has consumed smaller galaxies in the past. But piecing together the history of these galactic meals is a real challenge.

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The Milky Way Broke one of its Arms

A contingent of stars and star-forming clouds was found jutting out from the Milky Way's Sagittarius Arm. Credit: NASA/JPL-Caltech

The Milky Way galaxy is our home, and yet in some ways, it is the least understood galaxy. One of the biggest challenges astronomers have is in understanding its large-scale structure. Because we’re in the midst of it all, mapping our galaxy is a bit like trying to map the size and shape of a wooded park while standing in the middle of it.

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Gaia Might Even be Able to Detect the Gravitational Wave Background of the Universe

Embry-Riddle researchers used data captured by the Gaia satellite (shown here in an artist’s impression) to determine the ages of stars. Credit: European Space Agency – D. Ducros, 2013
Embry-Riddle researchers used data captured by the Gaia satellite (shown here in an artist’s impression) to determine the ages of stars. Credit: European Space Agency – D. Ducros, 2013

The Gaia spacecraft is an impressive feat of engineering. Its primary mission is to map the position and motion of more than a billion stars in our galaxy, creating the most comprehensive map of the Milky Way thus far. Gaia collects such a large amount of precision data that it can make discoveries well beyond its main mission. For example, by looking at the spectra of stars, astronomers can measure the mass of individual stars to within 25% accuracy. From the motion of stars, astronomers can measure the distribution of dark matter in the Milky Way. Gaia can also discover exoplanets when they pass in front of a star. But one of the more surprising uses is that Gaia could help us detect cosmic gravitational waves.

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What Are Extrasolar Planets?

An exoplanet about ten times Jupiter's mass located some 330 light years from Earth. X-ray: NASA/CXC/SAO/I.Pillitteri et al; Optical: DSS; Illustration: NASA/CXC/M.Weiss

For countless generations, human beings have looked out at the night sky and wondered if they were alone in the Universe. With the discovery of other planets in our Solar System, the true extent of the Milky Way galaxy, and other galaxies beyond our own, this question has only deepened and become more profound.

And whereas astronomers and scientists have long suspected that other star systems in our galaxy and the Universe had orbiting planets of their own, it has only been within the last few decades that any have been observed. Over time, the methods for detecting these “extrasolar planets” have improved, and the list of those whose existence has been confirmed has grown accordingly (over 4000 and counting!)

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Astronomers Improve Their Distance Scale for the Universe. Unfortunately, it Doesn't Resolve the Crisis in Cosmology

The accuracy of Gaia distance measurements. Credit: ESA

Measuring the expansion of the universe is hard. For one thing, because the universe is expanding, the scale of your distance measurements affects the scale of the expansion. And since light from distant galaxies takes time to reach us, you can’t measure what the universe is, but rather what it was. Then there is the challenge of the cosmic distance ladder.

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Some of the Milky Way’s oldest stars aren’t where they’re expected to be

Representation of the orbit of the star 232121.57-160505.4. Credit: Cordoni, et al

One of the ways we categorize stars is by their metallicity. That is the fraction of heavier elements a star has compared to hydrogen and helium. It’s a useful metric because the metallicity of a star is a good measure of its age.

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