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Shockwaves Are Driving This Galaxy To Its Imminent Doom

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This galaxy looks like our own Milky Way, except for a pair of spiral arms emerging out of the galactic plane. That one anomaly is enough to radically change the evolution of NGC 4258, as powerful jets are generating shockwaves driving gas right out of the galaxy and slowing star growth to a crawl.

Top image: NGC 4258, where X-rays are blue (Chandra X-ray Observatory), radio data is purple (Karl Jansky Very Large Array), optical data are yellow and blue (Hubble Space Telescope), and infrared data are red (Spitzer Space Telescope). Credit: NASA/CXC/JPL-Caltech/STScI/NSF/NRAO/VLA

Approximately 23 million light-years away, the spiral galaxy NGC 4258 (M106) contains not only the normal curving arms of dust and stars that characterize spiral galaxies, but also a pair of arms stretching beyond the galactic plane. A supermassive black hole dominating the center of the galaxy is spewing jets of high-energy particles. As the jets strike the galactic disk, they generate shockwaves that blast through the arms, heating enough gas to fuel 10 million suns.


So much of the universe is revealed when you're willing to look in wavelengths beyond the optical spectrum. When astronomers remapped optical, X-ray, radio, and infrared wavelengths to explore this spiral galaxy, they found two anomalous arms reaching out of the galactic plane. By stripping away the chaos of optical light, they were better able to investigate the central black hole and its powerful jets.


Hotspots glow brightly where jets from the central black hole drive shockwaves through dust and gas in the galactic plane. X-rays are blue (Chandra X-ray Observatory), and infrared data are red and green (Spitzer Space Telescope). Image credit: NASA/CXC/NASA/JPL-Caltech

Peering at the galaxy in different wavelengths of light differentiates the various processes. The radio data from Karl Jansky Very Large Array reveals the powerful jets driven by the black hole. In X-rays revealed by the Chandra X-ray Observatory, bubbles of hot gas emerge above and below the galaxy, tracing out gas heated to millions of degrees as it is driven out of the galactic plane. Hydrogen molecules are revealed in infrared, heated from -28°C to 760°C by the shockwaves, glowing brightly for the Spitzer Space Telescope.


This galaxy is fascinating in part because it is both so similar and so different than the Milky Way. The central black hole is about ten times larger than the one in our galaxy, consuming materials at a faster rate. The relative scarcity of gas in the galaxy has already had a noticeable impact on the birth rate of new stars — NGC 4258 is producing stars at just a tenth of the rate of star growth in the Milky Way. That's a paltry production rate of just 0.08 solar masses per year of stars, while a robust galaxy can produce up to 3 solar masses per year.

All the gas being driven out of the galaxy has a noticeable impact on the galaxy's evolution: fewer stars are born as the stellar nurseries are starved of dust and gas. Astronomers currently estimate that within about 300 million years — an eyeblink of time, astronomically speaking — the remaining gas will be driven from the galaxy. When that happens, the galaxy will transition from a beautiful spiral galaxy with stars brightly twinkling in its arms into a old, fading lenticular galaxy populated by slowly-dying red giants.


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