How Do Galaxies Die?

Everything eventually dies, even galaxies. So how does that happen? Time to come to grips with our galactic mortality. Not as puny flesh beings, or as a speck of rock, or even the relatively unassuming ball of plasma we orbit.

Today we’re going to ponder the lifespan of the galaxy we inhabit, the Milky Way. If we look at a galaxy as a collection of stars, some are like our Sun, and others aren’t.

The Sun consumes fuel, converting hydrogen into helium through fusion. It’s been around for 5 billion years, and will probably last for another 5 before it bloats up as a red giant, sheds its outer layers and compresses down into a white dwarf, cooling down until it’s the background temperature of the Universe.

So if a galaxy like the Milky Way is just a collection of stars, isn’t that it? Doesn’t a galaxy die when its last star dies?

But you already know a galaxy is more than just stars. There’s also vast clouds of gas and dust. Some of it is primordial hydrogen left from the formation of the Universe 13.8 billion years ago.

All stars in the Milky Way formed from this primordial hydrogen. It and other similar sized galaxies produce 7 bouncing baby stars every year. Sadly, ours has used up 90% of its hydrogen, and star formation will slow down until it both figuratively, and literally, runs out of gas.

The Milky Way will die after it’s used all its star-forming gas, when all of the stars we have, and all those stars yet to be born have died. Stars like our Sun can only last for 10 billion years or so, but the smallest, coolest red dwarfs can last for a few trillion years.

The Andromeda Galaxy will collide with the Milky Way in the future. Credit: Adam Evans
The Andromeda Galaxy. Credit: Adam Evans

That should be the end, all the gas burned up and every star burned out. And that’s how it would be if our Milky Way existed all alone in the cosmos.

Fortunately, we’re surrounded by dozens of dwarf galaxies, which get merged into our Milky Way. Each merger brings in a fresh crop of stars and more hydrogen to stoke the furnaces of star formation.

There are bigger galaxies out there too. Andromeda is bearing down on the Milky Way right now, and will collide with us in the next few billion years.

When that happens, the two will merge. Then there’ll be a whole new era of star formation as the unspent gas in both galaxies mix together and are used up.

Eventually, all galaxies gravitationally bound to each other in this vicinity will merge together into a giant elliptical galaxy.

We see examples of these fossil galaxies when we look out into the Universe. Here’s M49, a supermassive elliptical galaxy. Who knows how many grand spiral galaxies stoked the fires of that gigantic cosmic engine?

Eta Carinae shines brightly in X-rays in this image from the Chandra X-Ray Observatory.
Eta Carinae shines brightly in X-rays in this image from the Chandra X-Ray Observatory.

Elliptical galaxies are dead galaxies walking. They’ve used up all their reserves of star forming gas, and all that’s left are the longer lasting stars. Eventually, over vast lengths of time, those stars will wink out one after the other, until the whole thing is the background temperature of the Universe.

As long as galaxies have gas for star formation, they’ll keep thriving. Once it’s gonzo, or a dramatic merger uses all the gas in one big party, they’re on their way out.

What could we do to prolong the life of our galaxy? Let’s hear some wild speculation in the comments below.

Wow! Gas Bridge In The Universe Stretches 2.6 Million Light-Years Across

How the heck did all that gas get there? Researchers have discovered an astonishing amount of it bridging galaxies, stretching across a stream that is 2.6 million light-years across. This is more than a million light-years longer than a similar stream that was previously found in the Virgo Cluster.

“This was totally unexpected,” stated Rhys Taylor, a researcher at the Czech Academy of Sciences who led the research. “We frequently see gas streams in galaxy clusters, where there are lots of galaxies close together, but to find something this long and not in a cluster is unprecedented.”

The atomic hydrogen gas is about 500 million light-years away and was spotted with the William E. Gordon Telescope at the Arecibo Observatory in Puerto Rico.

Its origins are unknown, but one hypothesis postulateas that a larger galaxy passed close to smaller galaxies in the distant past, drawing out the gas as the larger galaxy moved apart again. Alternately, the large galaxy could have pushed through the group and disturbed the gas within it.

The research will be published shortly in the Monthly Notices of the Royal Astronomical Society.

Source: Royal Astronomical Society

What Are Comet Tails?

Comets are renowned for their big beautiful tails that stretch across the sky. But what’s in those things, anyway? And how can comets get multiple tails?

In the past, humans generally used one of two greetings for comets:
1. Dear God, what is that thing? Terrible omens! Surely we will all die in fire.
2. Dear God, what is that thing? Great omens! Surely we will all have a big party… where we all die in fire?

For example, the appearance of what came to be known as Halley’s comet in 1066 was seen as a bad omen for King Harold II. Conversely, it was a good omen for William the Conqueror.

Because of their tails and transitory nature, comets were long thought to be products of the Earth’s atmosphere. It wasn’t until the 1500s, when Tycho Brahe used parallax to determine a comet’s distance. He realized that they were Solar System objects, like planets.

So, good news, we no longer regard them as omens and everyone stopped panicking. Right? Wrong. When Comet Halley approached Earth in 1910, astronomers detected cyanide gas in its tail. French astronomer Camille Flammarion was quoted as saying the gas could “impregnate the atmosphere and possibly snuff out all life on the planet.” This caused a great deal of hysteria. Many bought gas masks and “comet pills” to protect themselves.

With the rise of photographic astronomy, it was found that comets often have two types of tails. A bright tail composed of ionized gas, and a dimmer one composed of dust particles. The ion tail always points away from the Sun. It’s actually being pushed away from the comet by the solar wind.

Comets often develop two tails as they near the sun - a curved dust tail and straight, ion tail. Credit: NASA
Comets often develop two tails as they near the sun – a curved dust tail and straight, ion tail. Credit: NASA

We now know that a comet’s ion tail contains “volatiles” such as water, methane, ammonia and carbon dioxide. These volatiles are frozen near the comet’s surface, and as they approach the Sun, they warm and become gaseous. This also causes dust on the comet’s surface to stream away. The heating of a comet by the Sun is not uniform.

Because of a comet’s irregular shape and rotation, some parts of the surface can be heated by sunlight, while other parts remain cold. In some cases this can mean that comets can have multiple tails, which creates amazing effects where different regions of a comet stream off volatiles.

Comet Lovejoy passing behind green oxygen and sodium airglow layers on December 22, 2011 seen from the space station. Credit: NASA/Dan Burbank
Comet Lovejoy passing behind green oxygen and sodium airglow layers on December 22, 2011 seen from the space station. Credit: NASA/Dan Burbank

These ion tails can be quite large, and some have been observed to be nearly 4 times the distance of the Earth from the Sun. And even though they fill a great volume, they are also pretty diffuse. If you condensed a comet’s tail down to the density of water, it wouldn’t even fill a swimming pool.

We also now know that there isn’t a clear dividing line between comets and asteroids. It’s not the case the comets are dirty snowballs and asteroids are dry rocks. There is a range of variation, and asteroids can gain dusty or gaseous tails and take on a comet-like appearance. In addition, we’ve also found comets orbiting other stars, known as exocomets.

And finally one last fact, the term comet comes from the Latin cometa, which indicated a hairy star.

So, what’s your favorite comet? Tell us in the comets below. And if you like what you see, come check out our Patreon page and find out how you can get these videos early while helping us bring you more great content!

Keck Spots A Galaxy Fueled With Ancient Gas

“Primordial hydrogen” sounds like a great name for a band. It’s also a great thing to find when you’re looking at a galaxy. This ancient gas is a leftover of the Big Bang, and astronomers discovered it in a faraway star-forming galaxy that was created when the universe was young.

A continuous stream of gas was likely responsible for a cornucopia of star formation that took place about 10 billion years ago, when galaxies were churning out starbirths at a furious rate.

The astronomers spotted the gas by using a quasar that lit up the fuel from behind. Quasars a handy tool to use if you want to illuminate something, because even though quasars don’t live for very long in cosmic terms — they occur when matter falls into a ginormous black hole — they are extremely bright. Since the gas absorbs the light at certain frequencies, the absorption lines that show up in spectrometers reveal information about the composition, temperature and density of the gas.

“This is not the first time astronomers have found a galaxy with nearby gas, revealed by a quasar. But it is the first time that everything fits together,” stated Neil Crighton, who is with the Max Planck Institute for Astronomy and Swinburne University and led the research. His team found the galaxy using the Keck I telescope in Hawaii.

The sun sets on Mauna Kea as the twin Kecks prepare for observing. Credit: Laurie Hatch/ W. M. Keck Observatory

“The galaxy is vigorously forming stars,” added Crighton, “and the gas properties clearly show that this is pristine material, left over from the early universe shortly after the Big Bang.”

Q1442-MD50 (as the galaxy is called) is 11 billion light years away from us — pretty close to the start of the universe about 13.8 billion years ago. The quasar that lit it up is called QSO J1444535+291905.

“Since this discovery is the result of a systematic search, we can now deduce that such cold flows are quite common,” stated Joseph Hennawi, the leader of the ENIGMA research group at the Max Planck Institute for Astronomy. “We only had to search 12 quasar-galaxy pairs to discover this example. This rate is in rough agreement with the predictions of supercomputer simulations, which provides a vote of confidence for our current theories of how galaxies formed.”

You can read more details in the article (which is in Astrophysical Letters) or in this preprint version on Arxiv.

Source: Keck Observatory

Supermassive Black Holes Keep Galaxies From Getting Bigger

It’s long been a mystery for astronomers: why aren’t galaxies bigger? What regulates their rates of star formation and keeps them from just becoming even more chock-full-of-stars than they already are? Now, using a worldwide network of radio telescopes, researchers have observed one of the processes that was on the short list of suspects: one supermassive black hole’s jets are plowing huge amounts of potential star-stuff clear out of its galaxy.

Astronomers have theorized that many galaxies should be more massive and have more stars than is actually the case. Scientists proposed two major mechanisms that would slow or halt the process of mass growth and star formation — violent stellar winds from bursts of star formation and pushback from the jets powered by the galaxy’s central, supermassive black hole.

Read more: Our Galaxy’s Supermassive Black Hole is a Sloppy Eater

“With the finely-detailed images provided by an intercontinental combination of radio telescopes, we have been able to see massive clumps of cold gas being pushed away from the galaxy’s center by the black-hole-powered jets,” said Raffaella Morganti, of the Netherlands Institute for Radio Astronomy and the University of Groningen.

The scientists studied a galaxy called 4C12.50, nearly 1.5 billion light-years from Earth. They chose this galaxy because it is at a stage where the black-hole “engine” that produces the jets is just turning on. As the black hole, a concentration of mass so dense that not even light can escape, pulls material toward it, the material forms a swirling disk surrounding the black hole. Processes in the disk tap the tremendous gravitational energy of the black hole to propel material outward from the poles of the disk.

NGC 253, aka the Sculptor Galaxy, is also blowing out gas but as the result of star formation (Image: T.A. Rector/University of Alaska Anchorage, T. Abbott and NOAO/AURA/NSF)
NGC 253, aka the Sculptor Galaxy, is also blowing out gas but as the result of star formation (Image: T.A. Rector/University of Alaska Anchorage, T. Abbott and NOAO/AURA/NSF)

At the ends of both jets, the researchers found clumps of hydrogen gas moving outward from the galaxy at 1,000 kilometers per second. One of the clouds has much as 16,000 times the mass of the Sun, while the other contains 140,000 times the mass of the Sun.

The larger cloud, the scientists said, is roughly 160 by 190 light-years in size.

“This is the most definitive evidence yet for an interaction between the swift-moving jet of such a galaxy and a dense interstellar gas cloud,” Morganti said. “We believe we are seeing in action the process by which an active, central engine can remove gas — the raw material for star formation — from a young galaxy,” she added.

The researchers published their findings in the September 6 issue of the journal Science.

Source: NRAO press release

ALMA Spots a Nascent Stellar Monster

Even though it comprises over 99% of the mass of the Solar System (with Jupiter taking up most of the rest) our Sun is, in terms of the entire Milky Way, a fairly average star. There are lots of less massive stars than the Sun out there in the galaxy, as well as some real stellar monsters… and based on new observations from the Atacama Large Millimeter/submillimeter Array, there’s about to be one more.

Early science observations with ALMA have provided astronomers with the best view yet of a monster star in the process of forming within a dark cloud of dust and gas. Located 11,000 light-years away, Spitzer Dark Cloud 335.579-0.292 is a stellar womb containing over 500 times the mass of the Sun — and it’s still growing. Inside this cloud is an embryonic star hungrily feeding on inwardly-flowing material, and when it’s born it’s expected to be at least 100 times the mass of our Sun… a true stellar monster.

The location of SDC 335.579-0.292 in the southern constellation of Norma (ESO, IAU and Sky & Telescope)
The location of SDC 335.579-0.292 in the southern constellation of Norma (ESO, IAU and Sky & Telescope)

The star-forming region is the largest ever found in our galaxy.

“The remarkable observations from ALMA allowed us to get the first really in-depth look at what was going on within this cloud,” said Nicolas Peretto of CEA/AIM Paris-Saclay, France, and Cardiff University, UK. “We wanted to see how monster stars form and grow, and we certainly achieved our aim! One of the sources we have found is an absolute giant — the largest protostellar core ever spotted in the Milky Way.”

Watch: What’s the Biggest Star in the Universe?

SDC 335.579-0.292 had already been identified with NASA’s Spitzer and ESA’s Herschel space telescopes, but it took the unique sensitivity of ALMA to observe in detail both the amount of dust present and the motion of the gas within the dark cloud, revealing the massive embryonic star inside.

“Not only are these stars rare, but their birth is extremely rapid and their childhood is short, so finding such a massive object so early in its evolution is a spectacular result.”

– Team member Gary Fuller, University of Manchester, UK

The image above, a combination of data acquired by both Spitzer and ALMA (see below for separate images) shows tendrils of infalling material flowing toward a bright center where the huge protostar is located. These observations show how such massive stars form — through a steady collapse of the entire cloud, rather than through fragmented clustering.

SDC 335.579-0.292 seen in different wavelengths of light.
SDC 335.579-0.292 seen in different wavelengths of light.

“Even though we already believed that the region was a good candidate for being a massive star-forming cloud, we were not expecting to find such a massive embryonic star at its center,” said Peretto. “This object is expected to form a star that is up to 100 times more massive than the Sun. Only about one in ten thousand of all the stars in the Milky Way reach that kind of mass!”

(Although, with at least 200 billion stars in the galaxy, that means there are still 20 million such giants roaming around out there!)

Read more on the ESO news release here.

Image credits: ALMA (ESO/NAOJ/NRAO)/NASA/JPL-Caltech/GLIMPSE

A Galaxy Grows Fat on Nearby Gas

If you live in the U.S. you may be enjoying a sultry summer day off in honor of Independence Day, or at least have plans to get together with friends and family at some point to partake in some barbecued goodies and a favorite beverage (or three). And as you saunter around the picnic table scooping up platefuls of potato salad, cole slaw, and deviled eggs, you can also draw a correlation between your own steady accumulation of mayonnaise-marinated mass and a distant hungry galaxy located over 11 billion light-years away.

Astronomers have always suspected that galaxies grow by pulling in material from their surroundings, but this process has proved very difficult to observe directly. Now, ESO’s Very Large Telescope has been used to study a very rare alignment between a distant galaxy and an even more distant quasar — the extremely bright center of a galaxy powered by a supermassive black hole. The light from the quasar passes through the material around the foreground galaxy before reaching Earth, making it possible to explore in detail the properties of the in-falling gas and giving the best view so far of a galaxy in the act of feeding.

“This kind of alignment is very rare and it has allowed us to make unique observations,” said Nicolas Bouché of the Research Institute in Astrophysics and Planetology (IRAP) in Toulouse, France, lead author of the new paper. “We were able to use ESO’s Very Large Telescope to peer at both the galaxy itself and its surrounding gas. This meant we could attack an important problem in galaxy formation: how do galaxies grow and feed star formation?”

A beam from the Laser Star Guide on one of the VLT's four Unit Telescopes helps to correct the blurring effect of Earth's atmosphere before making observations (ESO/Y. Beletsky)
A beam from the Laser Star Guide on one of the VLT’s four Unit Telescopes helps to correct the blurring effect of Earth’s atmosphere before making observations (ESO/Y. Beletsky)

Galaxies quickly deplete their reservoirs of gas as they create new stars and so must somehow be continuously replenished with fresh gas to keep going. Astronomers suspected that the answer to this problem lay in the collection of cool gas from the surroundings by the gravitational pull of the galaxy. In this scenario, a galaxy drags gas inwards which then circles around it, rotating with it before falling in.

Although some evidence of such accretion had been observed in galaxies before, the motion of the gas and its other properties had not been fully explored up to now.

Astronomers have already found evidence of material around galaxies in the early Universe, but this is the first time that they have been able to show clearly that the material is moving inwards rather than outwards, and also to determine the composition of this fresh fuel for future generations of stars. And in this particular instance, without the quasar’s light to act as a probe the surrounding gas would be undetectable.

“In this case we were lucky that the quasar happened to be in just the right place for its light to pass through the infalling gas. The next generation of extremely large telescopes will enable studies with multiple sightlines per galaxy and provide a much more complete view,” concluded co-author Crystal Martin of the University of California Santa Barbara.

This research was presented in a paper entitled “Signatures of Cool Gas Fueling a Star-Forming Galaxy at Redshift 2.3”, to appear in the July 5, 2013 issue of the journal Science.

Source: ESO news release

Galactic Close Call Leaves a Bridge of Gas

[/caption]

An ancient passing between two nearby galaxies appears to have left the participants connected by a tenuous “bridge” of hydrogen gas, according to findings reported Monday, June 11 by astronomers with the National Radio Astronomy Observatory (NRAO).

Using the National Science Foundation’s Green Bank Telescope in West Virginia — the world’s largest fully-steerable radio telescope — astronomers have confirmed the existence of a vast bridge of hydrogen gas streaming between the Andromeda galaxy (M31) and the Triangulum galaxy (M33), indicating that they likely passed very closely billions of years ago.

The Robert C. Byrd Green Bank Telescope (GBT) in West Virginia (NRAO/AUI)

The faint bridge structure had first been identified in 2004 with the 14-dish Westerbork Synthesis Radio Telescope in the Netherlands but there was some scientific dispute over the findings. Observations with the GBT confirmed the bridge’s existence as well as revealed the presence of six large clumps of material within the stream.

Since the clumps are moving at the same velocity as the two galaxies relative to us, it seems to indicate the bridge of hydrogen gas is connecting them together.

“We think it’s very likely that the hydrogen gas we see between M31 and M33 is the remnant of a tidal tail that originated during a close encounter, probably billions of years ago,” said Spencer Wolfe of West Virginia University. “The encounter had to be long ago, because neither galaxy shows evidence of disruption today.”

The findings were announced Monday at the 220th Meeting of the American Astronomical Society in Anchorage, Alaska. Read more on the NRAO website here.

States of Matter

Solid, liquid, gas … those are the states of matter we’re thoroughly familiar with, but what makes for a state of matter? And are there other states of matter?

Since people first made distinctions between them, the states of matter were defined by how the matter behaved, in bulk; so a solid had a fixed shape (and volume), a liquid a fixed volume (but changed shape to fit the container it was in), and a gas expanded to fill its container. Once we realized that matter is made up of atoms (and molecules), the states of matter were distinguished by how the molecules (or atoms, in an element) behaved: in solids they are both close by and in a fixed arrangement (e.g. in crystals), in liquids close by but the arrangement is not fixed, and in gases not close by (so no particular arrangement).

But what about plasma? Sorta like a gas – so as it fills any container it’s in, it’s a gas – but not (the ions and electrons interact in completely different ways, in a plasma, than molecules (or atoms) do in a solid, liquid, or gas). Hence, plasma is the fourth state of matter.

Things got a bit more complicated as scientists studied matter more carefully.

For example, if you heat water in a strong, but transparent, container, above a certain temperature (and pressure) – called the critical temperature (critical pressure) – the liquid and gas states become one … the water is now a supercritical fluid (you may have seen this demonstrated, in a chemistry class perhaps, though likely not with water!).

Then there’s the distinction between crystals (crystalline state) and glasses (glassy state); both seem very solid, but the arrangement of molecules in a glass is more like that of molecules in a liquid than those in a crystal … and glasses can flow, just like liquids, if left for a long enough time.

Is there a ‘fifth state of matter’? Yes! A Bose-Einstein condensate (BEC) … which is like a gas, except that the constituent atoms are all (or mostly) in the lowest possible quantum state … so a BEC has bulk properties quite unlike those of any other state of matter (quantum behavior become macroscopic).

In astrophysics, there are quite a few exotic states of matter; for example, in white dwarf stars matter is prevented from further (gravitational) collapse by electron degeneracy pressure; the same sort of thing happens in neutron stars, except that its neutron degeneracy pressure (there may also be an even more extreme state of matter, held up by quark degeneracy pressure!). There’s also a counterpart to ordinary plasmas: quark-gluon plasma (in an ordinary plasma made of hydrogen the atoms are broken into electrons and protons; in a quark-gluon plasma protons and neutrons ‘melt’ into their constituent quarks and gluons).

Are there related Universe Today stories? Sure! For example: Forget Neutron Stars, Quark Stars May Be the Densest Bodies in the Universe, Schwarzschild Radius, and Next Generation Magnetoplasma Rocket Could be Tested on Space Station.

States of matter, including some exotic ones, is something you’ll find discussed in Astronomy Cast; for example this Questions Show.

Sources:
Wikipedia
Purdue University
New York University
Wikipedia: Bose-Einstein Condensate