What Is the Center of Our Galaxy Like?

View Filtered Articles View All Articles

Even if we could explore there, it would take us more than 25,000 years to reach it.

We tend to think of our experience in the Orion Spur of the Milky Way as typical. Even in science fiction films, when traveling between stars, every sky looks the same. In reality, our galaxy isn’t quite so uniform.

Zoom into the Hubble Space Telescope view of the Milky Way’s dense galactic core. Hubble’s near-infrared vision pierced the dusty heart of the galaxy to reveal more than half a million stars in its nuclear star cluster, the most massive and densest stellar cluster in the galaxy. This region is so packed with stars, it is equivalent to having 1 million suns crammed into the volume of space between us and our closest stellar neighbor, Alpha Centauri, 4.3 light-years away. The star cluster surrounds the Milky Way’s central supermassive black hole, which is about 4 million times the mass of the Sun. CREDIT: NASA, ESA, and G. Bacon (STScI).

Milky Way's galactic core — Hubble's infrared vision reveled more than half a million stars at the core of the Milky Way. **CREDIT:** NASA, ESA, and the Hubble Heritage Team (STScI, AURA).

If you lived in the center of the Milky Way, you would look up at a sky thick with stars, up to 1 million times denser than we’re used to seeing. The closest star to our sun is about four light-years away; in the center of the galaxy, stars are only 0.4–0.04 light-years apart. In the inner 10,000 light-year region of the Milky Way, the galaxy’s spiral arm structure has broken down and transformed into a “bulge” of stars. At its heart—and the dominant force in that area of the galaxy—is a black hole one million times the mass of the Sun, called Sagittarius A* (pronounced “Sagittarius A star”).

Sleeping Giant

Black hole-powered Jet in galaxy M87 — A black-hole-powered stream of material is being ejected from the core of elliptical galaxy M87. The galaxy is the nearest example of an active galactic nucleus with a bright optical jet. **CREDIT:** NASA, ESA, and the Hubble Heritage Team (STScI, AURA).

Sagittarius A* is relatively calm compared to supermassive black holes in other galaxies. Astronomers aren’t sure why this is, and plan to use NASA’s James Webb Space Telescope to help uncover the mystery. Webb’s infrared light-detecting instruments can give us a clearer view of the tightly-packed region surrounding the black hole, as well as a more accurate measurement of its mass. Previous research has indicated that the mass of Sagittarius A* ranges on the low end of normal for galaxies the size of the Milky Way. Webb can examine why that is, and the relationship between a black hole and the matter surrounding it, in part by studying supermassive black holes in other galaxies.

Looking Inward and Outward

Active galactic nuclei (AGN) are a type of extremely bright galaxy core, fueled by supermassive black holes actively “consuming” large amounts of infalling cosmic matter. Astronomers plan to test their theories about the nature of AGN by observing the center of the Milky Way and other galaxies with Webb. Are these bright black holes triggered by events occurring within the centers of galaxies, or by mergers between galaxies?

Webb’s investigations of our own galaxy’s central black hole and the relationship between black holes and galaxy evolution could help solve a cosmic chicken-and-egg problem: Did black holes come first and galaxies form around them, or did galaxies form first and develop black holes? Or did the galaxies and black holes develop together?

Last Updated: October 15, 2021

Keywords: Black Holes Galaxies Milky Way Center

What Is the Center of Our Galaxy Like?

Even if we could explore there, it would take us more than 25,000 years to reach it.

Sleeping Giant

Looking Inward and Outward

???stnt_article.relatedArticles???