David Vs. Goliath — Galactic Struggle Leads To Transformation

This composite image, created from two different pointings of the Hubble Space Telescope, shows the barred spiral galaxy NGC 1512 (left) and the dwarf galaxy NGC 1510 (right). Both galaxies are about 30 million light-years away from Earth and currently in the process of merging. At the end of this process NGC 1512 will have cannibalized its smaller companion. Credit: ESA/Hubble, NASA

Relationships change everyone involved in subtle and sometimes not-so-subtle ways. These two very different galaxies, the large barred spiral NGC 1512 and its tiny companion, the dwarf galaxy, NGC 1510, might look like separate entities, but it just ain’t so.  NGC 1512 is classified as a barred spiral because of the large bar of stars, gas and dust slicing through its center. But despite their very different sizes, the gravity of each galaxy affects the other, causing slow changes in their appearances.

The bar in NGC 1512 acts as a cosmic funnel, channeling gas and dust required for star formation from the outer ring into the heart of the galaxy. This pipeline of material, seen as the dark, curling strands in the photo, fuels intense star birth in a bright, blue, shimmering inner disk 2,400 light years across called a circumnuclear starburst ring. Both the bar and the starburst ring are partly the result of a merger between the two galaxies that’s been in progress for, get this, 400 million years. Next time, I’m merging at rush hour I’ll try to keep a better perspective.

In this wider field of view and deeper photo, you can see how distorted NGC 1512’s spiral arms are especially where they cross by the dwarf galaxy, NGC 1510 (right). NGC 1512 is a barred spiral galaxy about 70,000 light-years across, located some 30 million light-years away from Earth in the southern constellation of Horologium. Credit: NASA/JPL-Caltech

NGC 1512 is also home to a second, more serene, star-forming region in its outer ring that appears as dozens of blue and pink knots, where large swathes of hydrogen gas are glowing under intense radiation from nearby, newly formed stars. Our own galaxy has lots of these, one of the most best known is the Orion Nebula.

Deep photos show that the barred galaxy extends way beyond the outer ring with lots of malformed, tendril-like arms wrapping around the dwarf companion. Their crazy, warped appearance is thought to be caused by strong gravitational interactions with NGC 1510. As you’ve probably already guessed,  the little guy’s also getting beat up in the process.

The constant tidal tugging from its neighbor has swirled up the gas and dust in NGC 1510 and kick-started star formation that is even more intense than in NGC 1512. This causes the galaxy to glow with the blue hue of hot new stars.

NGC 1510 is not the only galaxy to have experienced the massive gravitational tidal forces of NGC 1512. Observations made in 2015 showed that some of the outer, spidery arms were once part of a separate, older galaxy. This galaxy was ripped apart and absorbed by NGC 1512, just as it’s doing now to NGC 1510.

Each gives a little and gets a little. Together, the pair demonstrate how gravity can not only change the shapes of closely-paired galaxies but also how it can rejuvenates star-making in the process.

6 Responses

  1. Wayne S.

    How would this compare with the inevitable Milkly Way-Andromeda collision? Have we seen any mergers of that magnitude, with two larger galaxies?

  2. Brian B Rajala

    Your column, your observations and explanations are amazing. Both my wife and I are continually impressed.

Comments are closed.