The Solar System boundary and the week in review (September 8-14)

Cthulhu at NASA Wallops, for the LADEE launch last weekend. (I didn't wear the hat the whole time. I'm not that weird.)

Cthulhu at NASA Wallops, for the LADEE launch last weekend. (I didn’t wear the hat the whole time. I’m not that weird.)

‘Twas a busy week!

  • High-resolution observations show how black hole jets churn galactic gas (Ars Technica): One portion of my PhD thesis involved galactic feedback. That’s the process by which jets from black holes at the center of galaxies push material away, potentially affecting star formation and other activity. This article addressed the observation of galactic feedback, showing exactly where the hot jet of plasma from the black hole meets the colder atoms in galactic clouds. Very awesome stuff!
  • Parallel Earth and the Evil Matthew Hypothesis (Double X Science): I don’t know if Star Trek was the original source of the “evil twin from a parallel world” trope, but it’s the most famous. The idea is that there’s a mirror universe to ours, in which things are almost the same, but not quite. I discussed that trope in light of the multiverse, the concept that during rapid expansion right after the Big Bang, the Universe split into a number of disconnected regions that might obey different laws than our own.
  • Do-it-yourself science at GeekGirlCon (Galileo’s Pendulum): We’re still raising money to send a group of us to GeekGirlCon in Seattle next month! We’re willing to embarrass ourselves in public to accomplish this! However, the real purpose is to have hands-on science activities at the con.
  • Status of the book-in-progress (Galileo’s Pendulum): On a more somber note, I have suspended work on my book indefinitely and released my agent. I haven’t completely given up on either the book or getting it published, but the frustrations around the whole process have exhausted me, so it’s time for a break.
  • Cosmic coincidence and a potato eclipse (Double X Science): The Moon is nearly the same size as the Sun in our sky, which has led to all sorts of mystical musings and apocalyptic fears, especially during eclipses. However, that appearance is a coincidence, which we can understand using simple geometry. What’s even more fun to contrast our Moon to Phobos, the larger of Mars’ two moons, which is much smaller than our own but manages to create its own eclipses.
  • Voyager 1 really has left the Solar System…probably (Ars Technica): Sometime last year, the venerable spacecraft Voyager 1 crossed into interstellar space. While there have been a lot of announcements along these lines (I compared the number with Spinal Tap drummers), this time the probe seems to have actually done it. The necessary measurement is the plasma density, which is much higher in interstellar space, but Voyager’s plasma instrument had been knocked out by a solar flare. Researchers pieced together the appropriate data from other instruments. There’s still an anomalous measurement that needs to be accounted for — the magnetic field doesn’t behave as predicted — but I think it’s pretty safe to say that’s an issue for theorists, not ambiguity about Voyager’s position. (See below for a discussion of whether Voyager has actually “left the Solar System” or not.)
  • Mapping the dark matter in the tiniest of galaxies (Galileo’s Pendulum): Dwarf spheroidal galaxies don’t look like galaxies at all. They have so few stars and so little gas or dust, they’re nearly see-through, yet they have as much as 1000 times more dark matter than ordinary matter. (In regular galaxies, dark matter is more like 10 times the amount.) Two astronomers analyzed the motion of stars within dwarf spheroidals to see if they could map the distribution of dark matter, and they found something similar to what is seen in larger galaxies.
  • Finally, I participated in the Weekly Space Hangout, sponsored by Universe Today and CosmoQuest. I joined hosts Fraser Cain and Nicole Gugliucci, along with Amy Shira Teitel, David Dickinson, and Nancy Atkinson to talk about the space and astronomy news from the last week. The whole thing is archived at Google+, or you can watch the video on YouTube.

Where’s the edge of the Solar System?

Returning to Voyager 1, I think stories about its passage into interstellar space fell into two major categories: those saying “Voyager 1 has left the Solar System!” and variations on “Stop saying Voyager 1 has left the Solar System!” Despite what the headline on my story said, the second group of people (which includes writers I respect like Phil Plait and Amy Shira Teitel) is correct: the Solar System includes the Oort Cloud, a diffuse region of icy bodies loosely bound to the Sun by gravity.

A radio image of Voyager 1, as seen by the Very Long Baseline Array (VLBA) and the Green Bank Telescope. Click for a larger image and more information. [Credit: Alexandra Angelich, NRAO/AUI/NSF]

A radio image of Voyager 1, as seen by the Very Long Baseline Array (VLBA) and the Green Bank Telescope. Click for a larger image and more information. [Credit: Alexandra Angelich, NRAO/AUI/NSF]

However, if you want to say Voyager has left the Solar System, I’ll back you up: the boundary between the Oort Cloud and the “rest of the galaxy” isn’t very well defined. Gravity technically extends forever, though it weakens substantially with larger distances. As a result, the Oort Cloud is a fuzzy edge, and one we can’t measure. Is the end of the Solar System the point where the last Oort Cloud body resides?

Now, I agree with the pedants that the Oort Cloud truly does define the end of the Sun’s influence, and therefore is the edge of the Solar System. But the magnetic boundary of the Solar System, which is arguably the more important one from the point of view of astronomy, is defined by the edge of the heliopause, where the solar wind hits interstellar gas. That boundary, while it fluctuates with solar weather, is a much clearer division, and one we could conceivably measure near other stars.

So, I’m a both/and kind of guy in this case. Since there’s no single, sharp boundary between the Solar System and “everything else”, let’s just say there are two edges: one for the Sun’s electromagnetic influence (the heliopause), and one for its gravitational influence (the Oort Cloud). Voyager crossed the first one, but won’t reach the second one for 300 years. Now, can we get back to talking about how awesome Voyager is?


The week in review (August 18-24)

Granulation on the surface of the Sun, created by rising bubbles of hot plasma. Fluctuations in these bubbles can be measured on distant stars, which provides a way to calculate the stars' surface gravity. [Credit: Hinode JAXA/NASA/PPARC]

Granulation on the surface of the Sun, created by rising bubbles of hot plasma. Fluctuations in these bubbles can be measured on distant stars, which provides a way to calculate the stars’ surface gravity. [Credit: Hinode JAXA/NASA/PPARC]

I’ve been remiss in blogging at Bowler Hat Science, largely because…well, I’ve been writing too much elsewhere. So, I’m going to try something different: instead of blogging each new article I write in a separate entry, I’ll write a single post summarizing everything in one go.

  • How I learned to stop worrying and love tolerate the multiverse (Galileo’s Pendulum): My explanation of cosmology involving parallel universes is a response to a piece placing the multiverse in the same category as telepathy. While I’m not a fan of the multiverse concept, I reluctantly accept that it could be a correct description of reality.
  • An Arguably Unreal Particle Powers All of Your Electronics (Nautilus): Electrons in solids behave differently than their wild cousins. In some materials, the electronic and magnetic properties act as though they arise from particles that are lighter or heavier than electrons, or multiple types of particles with strange spins or electric charges. Are these quasiparticles real?
  • Kepler finds stars’ flickers reveal the gravity at their surface (Ars Technica): The Kepler observatory’s primary mission was to hunt for exoplanets, but arguably it’s been equally valuable for studying stars. A new study revealed a way to measure a star’s surface gravity by timing short-duration fluctuations — the rippling of hot plasma bubbles on the surface known as granulation (see above image).
  • Destruction and beauty in a distant galaxy (Galileo’s Pendulum): The giant galaxy M87 has a correspondingly huge black hole at its heart. That black hole in turn generates an enormous jet of matter extending 5,000 light-years, which fluctuates in a way we can see with telescopes. In that way, an engine of destruction shapes its environment and produces a thing of beauty.
  • The Freaky Celestial Events We See—and the Ones We Don’t (Nautilus): In another faraway galaxy, a black hole destroyed a star, producing a burst of gamma rays that lingered for months. This event is the only one of its kind we’ve yet seen, prompting the question: how do we evaluate events that are unique? How can we estimate how likely they truly are, especially if we’re seeing them from a privileged angle?
  • This isn’t writing, but after listing two black hole articles in a row, it seems a good time to advertise my Introduction to Black Holes online class in October! Sign up to learn all* about black holes. *All = what I can cover in four hours of class time.
  • Warp Speed? Not So Fast (Slate): Many articles have appeared over the last year or so profiling a NASA researcher, whose research supposedly could lead to a faster-than-light propulsion system. The problem: very little actual information about his work is known, and what he’s said publicly contradicts what we understand about general relativity and quantum physics.

Speaking of warp drives, I’ll conclude with this wonderful video of Patrick Stewart engaging with some obvious Star Trek fans.

I don’t spent a lot of time thinking about the multiverse: the possible existence of regions of the cosmos that have never been connected to ours at any time, and may never be in the future. That’s because those parallel pocket universes aren’t directly detectable, and may never be even indirectly detectable, putting them into a category that’s hard for a scientist to deal with. However, inflation — the extremely rapid expansion of the Universe in its earliest instants — almost certainly would produce those pocket universes, so I’ve reluctantly come to terms with the existence of the multiverse, on the principle that the alternative ideas are largely problematic.

Some physicists have gone a bit farther with the multiverse idea. Since our Universe has the correct physical/chemical properties to harbor life (self-evidently, since we’re here to talk about it), and those properties depend on a delicate balance of physical parameters, then maybe the multiverse can help explain what makes our pocket universe habitable. If those other pocket universes have different physical parameters, maybe the set ours has came about by a random process: no need for “fine-tuning”. However, as I argue in a new piece for the Nautilus blog, the fine-tuning problem is separate from the question of the multiverse, and philosophy won’t provide the solution to either.

We know that the universe is capable of supporting life, and that any physical parameters must be consistent with that obvious fact. Beyond that, we can’t go yet: We have no more evidence for multiverses than we have evidence for life beyond Earth—though it’s reasonable to think both exist. The uncomfortable possibility is that there are other pocket universes, but we’ll only ever know about them indirectly. That doesn’t make them any less real, just discomforting. [Read more…]

On the multiverse, metaphysics, and meaning