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Merging galaxies NGC 2207 and IC 2163 as observed by NASA's Spitzer Space Telescope (infrared: red) and the Hubble Space Telescope (visible: blue/green). Credit: NASA/JPL-Caltech/STScI/Vassar 

Star Stuff: Happy Halloween from the BOOniverse

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Oct 25, 2017

Star Stuff is a weekly column by rocket scientist & 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.

I’m turning the tables this week. Instead of galaxy gazing and pondering the beauty of the universe, what follows is my version of a haunted house of the cosmos - a fright night of big bang proportions. We’ll begin with some relatively benign, yet spooky celestial sights before moving on to stranger things (natch) and then rounding it out with our galaxy's violent past, present, and future.

Ghost Nebula. Credit: Adam Block, Mt. Lemmon SkyCenter, University of Arizona

First up, is the Ghost Nebula, a perennial favorite for setting the celestial spooky mood. This apparition is part of a much larger structure known as the Cepheus Flare molecular cloud complex. Located over 1,200 light-years away in the direction of theconstellation Cepheus (between the Little Dipper and Cassiopeia in the northern sky), the full nebula spans over 2 light-years across. New stars are actively being born in the denser pockets of gas and dust shown here, including a baby binary system in the lower right corner that is just about to go “BOO!”

Ghosts aren’t the only things haunting our skies this time of year, the Witch Head Nebula is also lurking about as the constellation Orion begins to show itself more and more. Formally known as IC 2118, this nebula is just off to the right of Orion’s knee (or foot) marked by the blue giant star, Rigel. Also a star-forming region, the nebula itself glows brightly in infrared light (colored green here) and spans over 50 light-years in length. Zooming out a bit allows us to see the full nebula (now blue as seen in infrared plus visible light), which I like to imagine as the “wicked witch of the winter” screaming at Rigel to turn out the lights so she can scare the neighborhood kids already.

Witch Head Nebula seen in infrared (left) and infrared+visible light (right). Credit: NASA/JPL-Caltech (left) and Rogelio Bernal Andreo (Deep Sky Colors) (right).

Okay one last spooky nebula for the road: the Hourglass Nebula. This nebula sees all. It knows what you did last summer and it is not amused. This “eye on the sky” was formed by a dying star over 8,000 light-years away in the direction of the constellation Musca, visible only from the southern hemisphere. Its structure is a mystery as astronomers aren’t exactly sure how it formed. Planetary nebula occur when low-mass stars, like our sun, exhaust their hydrogen cores and puff up to become red giants. Their outer layers then get spun off in all directions due to stellar winds. Each nebula has a unique shape based on the behavior of these winds and the star’s environment. The colors in this image represent the chemical composition of the nebula: ionized nitrogen (red), hydrogen (green), and doubly-ionized oxygen (blue).

Hourglass Nebula (left), Harvard computers (right) Credit: NASA/JPL-Caltech/ESA, the Hubble Heritage Team (STScI/AURA) and Harvard College Observatory/Wikimedia Commons

The Hourglass’s formal name is MyCn 18, named after Margaret Mayall (My) and Annie Jump Cannon (Cn) who first discovered it in the early 1900’s during their work as “computers” at the Harvard Observatory. While it’s seriously freaky that the laws of physics produced such a terrifying shape, I also like to think this nebula represents all the historical women in science who are keeping an eye on things to make sure their contributions are not forgotten. In fact, I should probably just go ahead and make “universal feminist” t-shirts with this image. Stay tuned for my Etsy store.

Let’s talk about some more active hazards in the Universe now. Last week, I wrote about a star that eats its own planets and given that there are over 100 billion stars in our galaxy alone, I’m willing to bet there are a lot more like it. As if black holes weren’t enough to deal with, now we have to worry about stars too?

Speaking of black holes though, they are pretty much the epitome of celestial terror. Roaming monsters that you can’t see until you feel a slight tug, and then a stronger pull, and before you know it you’ve been spaghettified, never to be seen or heard from again? While black holes are indeed black, thanks to their immense gravity that doesn’t even let light escape, it turns out they cause enough of a ruckus around them, that they can’t actually sneak up on us. This doesn’t mean that they are easy to spot, but we can find them by observing the effect they have on their surroundings.

Animation of the stars orbiting the center center of our galaxy for 20 years based on observations by the Keck Telescopes on Mauna Kea in Hawaii. 

My most favorite example of this is the black hole at the center of our galaxy. Astronomers believe that supermassive black holes (SMBHs) exist at the center of every galaxy, and the Milky Way is no different. We can observe SMBHs in various ways. Some are actively accreting material and we see them as active galactic nuclei (AGN), quasars, and blazars. Others are in between meals, but their strong gravitational field still gives them away. This animation shows how the stars at the very center of our galaxy are orbiting an apparent empty point in space. The laws of physics as laid out by Kepler, Newton, and Einstein allow us to estimate the mass required to shape the orbits of these stars as we observe them: ~4 million times the mass of our Sun. In keeping with the Halloween theme, SMBHs like ours are akin to that old run down house on the outskirts of town that your friends dared you to go knock on the door of but you never did because everyone had a friend of a friend of a friend who did it a few years back and was never heard from again.

What’s darker than a black hole...figuratively speaking of course? How about some dark matter? Dark matter is currently believed to make up roughly a quarter of the Universe. That may not sound like much, but it’s five times more than the amount of matter you and I are made of. Like black holes, we can infer the presence of dark matter by how it gravitationally interacts with normal matter. However, unlike black holes, we still don’t know what it’s made of, how it’s distributed, where it came from, whether it changes over time, etc., etc., etc.. All we know is that it’s taunting us.

Gravitational lens of galaxy cluster SDSS J1038+4849. Credit: NASA/ESA

This image is 100% real and is the result of gravitational lensing, an effect of Einstein’s Theory of General Relativity. The two glowing yellow eyes of the smiley face are actually two massive elliptical galaxies, part of the affectionately nicknamed the Cheshire Cat galaxy group. They are 4.5 billion light-years away and are in the process of merging. The blue arcs outlining the face and smile are an entirely different story. They are in fact background galaxies another 3 billion light-years further away. Thanks to the mass of the closer galaxies, the light from the more distant galaxies is being bent and warped as it travels through space, resulting in the distorted image captured here.

Gravitational lenses are one lines of evidence for the presence of dark matter in the Universe. Based on the size and shape of the lensed galaxies, astronomers can calculate how much mass is in the foreground (eyeball) galaxies. The answer far exceeds the amount of mass we can “see” with our telescopes in the form of stars, gas, and dust. Therefore there must be additional matter we can’t see to produce the degree of lensing shown in the image.

Dark matter was first hypothesized to exist in the late 1800’s, but didn’t get much traction until the early 1900’s. The strongest observational evidence began to surface in the 1970’s thanks to the work of Vera Rubin who measured the rotational velocities of galaxies and showed that they were spinning much faster than the observed visible matter allowed for. (Think of it like seeing a carousel going at speeds you know to exceed the strength of the materials holding it together.) In keeping with my spontaneous feminist theme, from now on I’m going to imagine this particular gravitational lens is Vera Rubin’s ghost reminding us she should have received the Nobel Prize in Physics for her work in this area. 

If after all this, you still aren’t scared of the Universe, I have two words for you: galactic cannibalism. You read that right, cannibals in space. Every galaxy in the Universe is fated to either eat other or be eaten, or sometimes both. Our very own precious Milky Way is a cannibal and as I write this, it is in the process of consuming the Large and Small Magellanic clouds, among other things. There are entire theses that have been written about its most recent snack, the Sagittarius dwarf galaxy.

Artist's impression of the Sagittarius dwarf galaxy being accreted by the Milky Way. Credit: Amanda Smith, Institute of Astronomy, University of Cambridge

This process happens on time scales of millions to billions of year so we aren’t currently in any danger from this devious behavior. However, the Milky Way and the Andromeda are on a collision course, cannibal versus cannibal. Over the next four billion years we will draw closer and closer together, eventually tearing each other apart gravitationally and spewing gas and dust trails over millions of light-years in all directions. Bizarrely, the chances of any two stars colliding are extremely rare, but that doesn’t mean things won’t get messy. There’s no telling where Earth might end up once the process begins. We could get captured by another star or flung into a gravitational pinball machine or thrown out of the fun entirely on an escape trajectory, never to know the warmth of a sun again.

Here's hoping you'll have enough Halloween candy to comfort you at the cold, dark end of life as we know it.