spiral galaxy M81
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Spiral Galaxy M81. Credit: Subaru Telescope (NAOJ), Hubble Space Telescope, Roberto Colombari, Robert Gendler

Star Stuff: I can't stop gazing at these gorgeous galaxies

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Sep 3, 2019, 7:57 AM EDT (Updated)

Star Stuff is a weekly column by rocket scientist and astrophysicist Summer Ash highlighting some amazing things happening every day on and off the planet, especially great science done by and/or for women. She harnesses her science communication powers to smash the patriarchy and advocate for equality and inclusion across all time and space. Throwdowns with pseudoscience may occur.

Today is for some good old-fashioned galaxy gazing, with a science chaser. 

First of all, if you don’t already know about Astronomy Picture of the Day (APOD), go bookmark it, subscribe to the RSS, download the app, etc. I’ll wait.

Okay, now get ready to drink in some gorgeous galaxies that were imaged recently by the Hubble Space Telescope. They are each stunning in their own way, and they each have something to tell us about galaxy formation and evolution.

First up is Messier 81, aka NGC 3031, aka Bode's Galaxy. As you can tell, our naming system has evolved over time. Most commonly known as M81 (the 81st object in a catalogue created by Charles Messier), this spiral galaxy is one of the brightest galaxies we can see from Earth. It’s just under 12 million light-years away in the direction of the Big Dipper. In cosmic terms, that’s like being in a neighboring state. M81 is close in size to our own galaxy, the Milky Way, so it provides a great opportunity for us to observe how spiral galaxies grow and change. 

The overwhelming majority of galaxies live in groups, clusters, and superclusters. M81 is in the Virgo supercluster with us, but it is one of 34 galaxies in a separate group. It has a history of gravitational interactions with two nearby galaxies, M82 and NGC 3077, which has caused massive amounts of hydrogen gas to be strewn out among all three of them.

This image is a combination of optical observations by both Hubble and the Subaru Space Telescope run by the National Astronomical Observatory of Japan (NAOJ). Molecular gas radiates primarily at longer wavelengths, which is why it’s not visible here. What is visible, though, is the differentiation between young and old stars and a striking dust lane cutting across the top, left. Contrary to how we often label our water faucet taps, when it comes to light, blue is hotter than red. So the concentrations of blue in the outskirts of the galaxy are where hot, young blue stars are being born, and the inner yellow portions are where the older, cooler stars live. 

Fun fact: Those pink spots (while likely somewhat enhanced) really are pink thanks to the hydrogen gas in those regions feeding star formation. Hydrogen only has four wavelengths it can emit light in when it’s excited, the brightest of which is red. Combine that with the large amounts of broad-spectrum white light coming from the same areas and you get pink.

Let’s travel a little farther out to NGC 1512, which sits at a distance of 38 million light-years from us, over three times more distance than M81. Its designation means it’s the 1512th object in the New Galaxy Catalogue, which was compiled back in 1888, almost 100 years after Messier started his.

Spiral Galaxy NGC 1512 image taken by the Hubble Space Telescope

Spiral Galaxy NGC 1512. Credit: NASA, ESA, Hubble Space Telescope

Only viewable from the Southern Hemisphere, NGC 1512 is a spiral galaxy a little smaller than the Milky Way, but with a radically different structure. In contrast to the tightly wound arms of many spirals, NGC 1512 almost looks like one spiral galaxy encircling another. In fact, it's what we call a barred spiral, and a unique one at that. The outer ring holds its spiral arms, which are then linked to the nucleus by a tenuous bar of stars, dust, and gas emanating out from the center. The ginormous gap between the outer and inner structures is likely due to a previous interaction (or multiple interactions) with a neighboring dwarf galaxy that lives off to the right (not pictured here).

Here again you can see the tell-tale signs of active star formation in the blue and pink regions around the galactic center, while the outer ring shows a tapestry of dust lanes weaving in and out the pockets where hot, young stars are being born.

Now let’s triple our distance from Earth once more, jumping out to 150 million light-years to visit NGC 6753, a tightly coiled behemoth. This galaxy is dominated by a bright yellow center, with bright blue arcs interspersed throughout its spiral arms. New stars are still being produced in those blue areas, formed from the cooling, collapsing hydrogen gas we can’t see in visible light. Conversely, the nucleus is full of older, redder stars that show up as yellow here and radiate most of the energy in the similarly invisible wavelengths of infrared.

Spiral galaxy NGC 6753 imaged by the Hubble Space Telescope

Spiral galaxy NGC 6753. Credit: ESA/Hubble & NASA

NGC 6753 is actually of great interest to astronomers due to yet another wavelength this image doesn’t show: X-ray. Just like our Sun, most galaxies have a corona -- a region of super-hot gas surrounding their visible structure in a sort of spherical halo. Galaxy coronas have such low densities though that they are really hard to observe, except for galaxies that are massive enough and/or close enough for our X-ray telescopes to detect them, like NGC 6753. 

All three of these images are pieces of a greater puzzle about how structures first formed in the Universe and how they evolved to the distribution of matter we observe today: stars, galaxies, clusters, and superclusters. Each image is just a snapshot in time, and not even the same time at that. Looking out in space is also looking back in time. So we are seeing these galaxies as they were 12 million, 38 million, and 150 million years ago. Imagine taking photos as a tourist in Times Square and trying to understand how babies grow into teenagers, who then grow into adults. That's what astronomers are doing with instruments like Hubble. Luckily, even without being Time Lords, we have supercomputers to help us speed up, slow down, and even freeze time so we can compare simulated galaxies with the ones we physically observe and adjust our theories and models accordingly. 

It's thanks to these computer simulations that I can actually predict the future, which is already the past, for at least two of these three galaxies. As I mentioned earlier, both M81 and NGC 1512 are gravitationally interacting with neighboring galaxies. This process will end with each of them cannibalizing their lesser companions and morphing into less structured, bulbous, elliptical galaxies where star-formation will one day cease. SPOILERS: There will also be supermassive black hole mergers to keep things from getting too dull. 

Since no human will ever be able to experience that process in real time, I recommend just gazing some more at these beauties and letting the biological supercomputer that is your imagination with run wild. 


Spiral galaxies to drool over. Left to right: M81, NGC 1512, NGC 6753. Credit: NASA, ESA, Hubble Space Telescope, Subaru Space Telescope.

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