Ripples in the cosmic pond

I know I've said this before, so at the risk of ringing the changes on this once too many times: I find it endlessly fascinating how much we can figure out about the universe, sitting here on this little speck of rock circling a mediocre star in the arm of an average galaxy.

Three papers came out last week in Nature Astronomy that each individually might bowl you over with the scale of things; put together, they're kind of staggering. First we have a paper by a team led by Tiantian Yuan, of Australia’s ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D).  Entitled "A Giant Galaxy in the Young Universe with a Massive Ring," this research looks at a very unusual object -- a collisional ring -- that is eleven billion light years away.

Meaning we're seeing it as it was eleven billion years ago.

"It is a very curious object that we’ve never seen before," Yuan said, in a press release.  "It looks strange and familiar at the same time.  It is making stars at a rate fifty times greater than the Milky Way.  Most of that activity is taking place on its ring – so it truly is a ring of fire."

"The collisional formation of ring galaxies requires a thin disk to be present in the ‘victim’ galaxy before the collision occurs," added Kenneth Freeman of the Australian National University, who co-authored the paper.  "The thin disk is the defining component of spiral galaxies: before it assembled, the galaxies were in a disorderly state, not yet recognizable as spiral galaxies.  In the case of this ring galaxy, we are looking back into the early universe by eleven billion years, into a time when thin disks were only just assembling.  For comparison, the thin disk of our Milky Way began to come together only about nine billion years ago.  This discovery is an indication that disk assembly in spiral galaxies occurred over a more extended period than previously thought."

Yes, you read that right.  The images of this object are pictures of something that existed two billion years before the Milky Way formed.

The second paper is about an object that is even older and father away than the ring galaxy.  Titled "A Cold, Massive, Rotating Disk Galaxy 1.5 Billion Years After the Big Bang," by a team led by Marcel Neeleman of the Max Planck Institute for Astronomy, is estimated to be 12.3 billion light years away -- so this structure is not only the oldest disk galaxy ever observed, it also gives us incredible new data on the way galaxies in general form.

The authors write:

Massive disk galaxies like the Milky Way are expected to form at late times in traditional models of galaxy formation, but recent numerical simulations suggest that such galaxies could form as early as a billion years after the Big Bang through the accretion of cold material and mergers.  Observationally, it has been difficult to identify disk galaxies in emission at high redshift in order to discern between competing models of galaxy formation...  The detection of emission from carbon monoxide in the galaxy yields a molecular mass that is consistent with the estimate [that the galaxy's mass is] about 72 billion solar masses.  The existence of such a massive, rotationally supported, cold disk galaxy when the Universe was only 1.5 billion years old favours formation through either cold-mode accretion or mergers, although its large rotational velocity and large content of cold gas remain challenging to reproduce with most numerical simulations.

So the astrophysicists are going to be sifting through that data for quite some time.

The third, "The Recurrent Impact of the Sagittarius Dwarf on the Star Formation History of the Milky Way," by a team led by Tomás Ruiz-Lara of the Instituto de Astrofísica de Canarias, describes something pretty amazing about our own galaxy; the main disc is orbited by a dwarf galaxy (the Sagittarius Dwarf in the title) which has an elliptical orbit, so it at regular intervals pierces the disc of the Milky Way -- causing eddies that trigger a huge spike in star production.

"You have the Milky Way in equilibrium, mostly calm, and then when Sagittarius passed it was like throwing a stone in a lake," said Ruiz-Lara, in an interview with New Scientist.  "It created these ripples in the galaxy’s density, so some areas became more dense and started forming stars more efficiently...  Maybe without Sagittarius the solar system wouldn’t exist.  The timing works out, but there is no way for us to know for sure."

[Image is in the Public Domain courtesy of NASA, ESA, and The Hubble Heritage Team STScI/AURA]

Gradually the dwarf galaxy is losing energy and its orbit is pulled in tighter and tighter, making these collisions and bursts of star formation more frequent.  "It’s getting closer and closer, little by little over time, and in the end it will merge with the Milky Way," Ruiz-Lara said.

Not to worry, that won't happen for another billion-odd years.  So no need to run and see if your stellar collision insurance is paid up.

It's kind of mind-boggling when you think about it, that a bunch of primates who were not so long ago loping around on the African savanna trying not to get eaten by lions have found a way to see into the farthest reaches of the universe.  Not to get cocky about it, but that's pretty spectacular.  Only a hundred years ago we didn't even know for sure how big or how old the universe is; today we're looking into the depths of space, and back in time almost as far is is physically possible.

It brings to mind the wonderful quote by Carl Sagan: "We are a way for the cosmos to know itself."

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This week's Skeptophilia book recommendation of the week is a fun one: acclaimed science writer Jennifer Ackerman's The Bird Way: A New Look at how Birds Talk, Work, Play, Parent, and Think.

It's been known for some years that a lot of birds are a great deal more intelligent than we'd thought.  Crows and other corvids are capable of reasoning and problem-solving, and actually play, seemingly for no reason other than "it's fun."  Parrots are capable of learning language and simple categorization.  A group of birds called babblers understand reciprocity -- and females are attracted to males who share their food the most ostentatiously.

So "bird brain" should actually be a compliment.

Here, Ackerman looks at the hugely diverse world of birds and gives us fascinating information about all facets of their behavior -- not only the "positive" ones (to put an human-based judgment on it) but "negative" ones like deception, manipulating, and cheating.  The result is one of the best science books I've read in recent years, written in Ackerman's signature sparkling prose.  Birder or not, this is a must-read for anyone with more than a passing interest in biology or animal behavior.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]

Rings in the sky

Sometimes I enjoy mysteries just because they're mysteries.

I ran across an astronomical curiosity yesterday that I'd never heard of before, and one that has had no convincing explanation; a ring galaxy.  The most famous example is "Hoag's Object," a ring galaxy discovered by astronomer Arthur Hoag.  It's about six hundred million light years away -- so not exactly in our neighborhood -- but that hasn't stopped the Hubble Space Telescope from getting an amazing photograph of it:

Hoag's Object [Image is in the Public Domain, courtesy of NASA]

As you can see, it's a torus (donut) of stars with a bright, dense cluster in the middle, and a gap where there's not much in the way of anything.  The estimate is that it's a hundred thousand light years across, so a bit larger than the Milky Way.

The curiosity is the gap.  It's hard to imagine what would cause this arrangement of matter; the stars in the ring must be orbiting fast enough to compensate for the gravitational pull of the stars in the center, but why were there none orbiting with the right velocity to end up in between?  My first thought was that it might be something similar to what caused Cassini's Division in the rings of Saturn, but when I looked into this, it turns out that the physicists don't know what caused that, either.

Various ideas were fielded to explain the odd structure.  Hoag himself thought at first that it was a case of gravitational lensing -- the bending of light when it passes through a strong gravitational field between the emitter and observer.  Sometimes, if the heavy object causing the bending is right between the two, light passing around it gets deflected into a bullseye shape called an Einstein ring (because the great man predicted the effect before it was observed):

[Image is in the Public Domain courtesy of NASA]

Even though the two photographs look superficially alike, the explanation was discarded when it was found that the ring of Hoag's Object showed no distortion on a smaller scale, and also the ring and the bright spot at the center had exactly the same degree of red shift, which would not be the case if the light emitted by it had passed through a strong gravitational field.

Other explanations were also proposed and discarded.  Perhaps it was caused by a collision between galaxies -- but there's no evidence of that, and the object's amazing symmetry argues against its having been the product of a chaotic merger.  Another was that it was the result of bar instability, which is when the matter distribution of a barred spiral galaxy results in a gravity field that is insufficient to keep the whole thing together, resulting in the furthest ones getting flung outward in an ever-increasing bubble.  But the almost perfectly spherical nature of the center of Hoag's Object caused astrophysicists to dismiss that explanation, too.

Long story short, we still have no idea how Hoag's Object formed, or even what exactly it is.  Other ring galaxies are known, but they're extremely rare, accounting for less than one in a thousand observed galaxies.  Another curiosity is that the stars in Hoag's Object are all very young, very hot blue-white stars -- but no one knows if that's relevant or a coincidence.

So we're left with a mystery.  I will say, however, that whatever it is, Hoag's Object is beautiful.  The idea that even our best scientists can't explain it adds to the mystique.  And it further reinforces something I've said many times; if you get interested in science, you'll never be bored.  There will always be questions to answer.

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Long-time readers of Skeptophilia have probably read enough of my rants about creationism and the other flavors of evolution-denial that they're sick unto death of the subject, but if you're up for one more excursion into this, I have a book that is a must-read.

British evolutionary biologist Richard Dawkins has made a name for himself both as an outspoken atheist and as a champion for the evolutionary model, and it is in this latter capacity that he wrote the brilliant The Greatest Show on Earth.  Here, he presents the evidence for evolution in lucid prose easily accessible to the layperson, and one by one demolishes the "arguments" (if you can dignify them by that name) that you find in places like the infamous Answers in Genesis.

If you're someone who wants more ammunition for your own defense of the topic, or you want to find out why the scientists believe all that stuff about natural selection, or you're a creationist yourself and (to your credit) want to find out what the other side is saying, this book is about the best introduction to the logic of the evolutionary model I've ever read.  My focus in biology was evolution and population genetics, so you'd think all this stuff would be old hat to me, but I found something new to savor on virtually every page.  I cannot recommend this book highly enough!

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]