Revising Hubble

If I had to pick the most paradigm-changing discovery of the twentieth century, a strong contender would be the discovery of red shift by astronomer Edwin Hubble.

What Hubble found was that when he analyzed the spectral lines from stars in distant galaxies, the lines -- representing wavelengths of light emitted by elements in the stars' atmospheres -- had slid toward the red (longer-wavelength) end of the spectrum.  Hubble realized that this meant that the galaxies were receding from us at fantastic speeds, resulting in a Doppler shift of the light coming from them.

What was most startling, though, is that the further away a galaxy was, the faster it was moving.  This observation led directly to the theory of the Big Bang, that originally all matter in the universe was coalesced into a single point, then -- for reasons still unclear -- began to expand outward at a rate that defies comprehension.

There's a simple quantity (well, simple to define, anyhow) that describes the relationship that Hubble discovered.  It's called the Hubble constant, and is defined at the ratio between the velocity of a galaxy and its distance from us.  The relationship seems to be linear (meaning the constant isn't itself dependent upon distance), but the exact value has proven extremely difficult to determine.  Measurements have varied between 50 and 500 kilometers per second per megaparsec, which is a hell of a range for something that's supposed to be a constant.

And the problem is, the value has varied depending on how it's calculated.  Measurements based upon the cosmic microwave background radiation give one range of values; measurements using Type 1A supernovae (a commonly-used "standard candle" for calculating the distances to galaxies) give a different range.

Enter Kenta Hotokezaka of Princeton University, who has decided to tackle this problem head-on.  “The Hubble constant is one of the most fundamental pieces of information that describes the state of the universe in the past, present and future," Hotokezaka said in a press release.  "So we’d like to know what its value is...  either one of [the accepted calculations of the constant] is incorrect, or the models of the physics which underpin them are wrong.  We’d like to know what is really happening in the universe, so we need a third, independent check."

Hotokezaka and his team have found the check they were looking for in the collision of two neutron stars in a distant galaxy.  The measurements made of the gravitational waves emitted by this collision were so precise it kind of boggles the mind.  Adam Deller, of Swinburne University of Technology in Australia, who co-authored the paper, said, "The resolution of the radio images we made was so high, if it was an optical camera, it could see individual hairs on someone’s head 3 miles away."

[Image licensed under the Creative Commons ESA, Colliding neutron stars ESA385307, CC BY-SA 3.0 IGO]

Using this information, the researchers were able to narrow in on the Hubble constant -- reducing the uncertainty to between 65.3 and 75.6 kilometers per second per megaparsec.

Quite an improvement over 50 to 500, isn't it?

"This is the first time that astronomers have been able to measure the Hubble constant by using a joint analysis of a gravitational-wave signals and radio images,"  Hotokezaka said about the accomplishment of his team.  "It is remarkable that only a single merger event allows us to measure the Hubble constant with a high precision — and this approach relies neither on the cosmological model (Planck) nor the cosmic-distance ladder (Type Ia)."

I'm constantly astonished by what we can learn of our universe as we sit here, stuck on this little ball of spinning rock around an average star in one arm of an average galaxy.  It's a considerable credit to our ingenuity, persistence, and creativity, isn't it?  From our vantage point, we're able to gain an understanding of the behavior of the most distant objects in the universe -- and from that, deduce how everything began.

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This week's Skeptophilia book recommendation is pure fun for anyone who (like me) appreciates both plants and an occasional nice cocktail -- The Drunken Botanist by Amy Stewart.  Most of the things we drink (both alcohol-containing and not) come from plants, and Stewart takes a look at some of the plants that have provided us with bar staples -- from the obvious, like grapes (wine), barley (beer), and agave (tequila), to the obscure, like gentian (angostura bitters) and hyssop (Bénédictine).

It's not a scientific tome, more a bit of light reading for anyone who wants to know more about what they're imbibing.  So learn a little about what's behind the bar -- and along the way, a little history and botany as well.

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

Taking the temperature of the universe

There's something compelling about the things in our universe that are on a wildly different scale than we are.  The very tiny -- subatomic particles, atoms, even things as (comparatively) large as molecules -- boggle our minds by their bizarre behavior, a body of knowledge collectively known as quantum mechanics.  Likewise, the very large bowls us over by our positions in a cosmos that makes even the most arrogant and human-centric of us feel insignificant.

It's the large end of the scale that's been a fascination of mine for some time.  I remember as a teenager running into the classic 1977 video Powers of Ten, that starts hovering a meter above the hand of a sleeping man in a park, and then moves away from him at an increasing speed, moving ten times faster every ten seconds.  Before much time has elapsed -- and the whole video is under ten minutes long -- we are outside of the known universe, and our own "Local Group" of galaxies is a mere dot in the center of the screen.  Then we dive back down toward the sleeping man, this time covering ten times less distance every ten seconds, and finally are centered on a single proton in a carbon atom in one of his DNA molecules.

Since 1977, of course, we've learned a lot more about each end of the scale.  We now know that the universe itself is anisotropic -- the stars and galaxies are not uniformly distributed across space, but exists in superclusters and filaments, with enormous empty spaces in between -- accurately if spookily called "cosmic voids."  (One of them, the Boötes void, is nicknamed "The Great Nothing," and is so large that if the Sun was at the center of it, the night sky would be completely black, and we would not have had a telescope powerful enough to find out about the existence of other stars until the 1960s.)

[Image is licensed under the Creative Commons Richard Powell, Nearsc, CC BY-SA 2.5]

A piece of research published this week in the journal Astronomy and Astrophysics has added another piece to our understanding of the structure of the universe, but raised a number of questions as well -- which, of course, good research should always do.

The paper, entitled "Isotropy and Statistics of the Cosmic Microwave Background Radiation," is an analysis of data from the Planck spacecraft, which has taken measurements for years of the radiation spread across the cosmos that is the remnant of the first flash of light at the moment of the Big Bang.  You'd expect that it would be fairly uniform -- given that the Big Bang kind of happened everywhere at once -- but the curious result of the research is that there is a "warm hemisphere" and a "cold hemisphere" of the universe, as measured by the deviation of the temperature from the average of only slightly above absolute zero -- and weirder still, that in the middle of the "warm hemisphere" is a giant cold spot.

[Image courtesy of the Planck Telescope Project]

What's the most bizarre about this is that the data hovers right on the edge of statistical significance, but the pattern has been detected more than once and does not seem to be a random fluctuation.  If it's correct, it'll force a significant rethinking of our understanding of the structure of the universe -- and how it all started.

So there's your moment of "geez, we are really tiny" for today.  On the Planck map picture above, the entire Milky Way -- 53,000 light years across, composed of about 250 billion stars -- is a single minuscule dot.  All of which makes our little struggles on this Pale Blue Dot seem rather inconsequential, doesn't it?

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As will be obvious to any long-time readers of Skeptophilia, I have a positive fascination with things that are big and scary and can kill you.

It's why I tell my students, in complete seriousness, if I hadn't become a teacher I'd have been a tornado chaser.  There's something awe-inspiring about the sheer magnitude of destruction they're capable of.  Likewise earthquakes, hurricanes, wildfires...

But as sheer destructive power goes, there's nothing like the ones that are produced off-Earth.  These are the subject of Phil Plait's brilliant, funny, and highly entertaining Death From the Skies.  Plait is best known for his wonderful blog Bad Astronomy, which simultaneously skewers pseudoscience and teaches us about all sorts of fascinating stellar phenomena.  Here, he gives us the scoop on all the dangerous ones -- supernovas, asteroid collisions, gamma-ray bursters, Wolf-Rayet stars, black holes, you name it.  So if you have a morbid fascination with all the ways the universe is trying to kill you, presented in such a way that you'll be laughing as much as shivering, check out Plait's book.

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