Thursday, October 24, 2013

Science is Fun

On Tuesday I got to talk with Scott Ransom, an astronomer who works on the science of pulsars and gravity waves – a very different subfield from mine.  He was visiting from Virginia, where he is affiliated with the National Radio Astronomy Observatory and often uses the Green Bank Telescope.  After meeting individually with me and several other astronomers in my department, Ransom gave a well-attended colloquium lecture Tuesday afternoon.  It was a typical schedule for an academic visit.  But as I thought in detail about his research, I realized all over again what an extraordinary endeavor astrophysics is – and how glad I am to be a part of it.

Pulsars, the subject of Ransom’s research, are neutron stars.  Neutron stars are the collapsed cores of exploded stars that, when they were still shining, were several times more massive than our Sun.  The violent gravitational collapse that forms a neutron star ends with typically twice the mass of the Sun crushed into a sphere just six to eight miles wide.  An average neutron star’s surface gravity is a hundred billion times stronger than Earth’s.  If one were to hit Earth (impossible since we know there are none within several light years: they would be easily visible on our X-ray sky maps), the strong rock and iron of which our lovely planet is made would be like cotton candy.  Earth would be effortlessly crushed and devoured by the neutron star’s relentless gravity, until it was reduced to a hot, ultra-dense layer roughly half an inch thick coating the surface of the neutron star.

But that’s all old hat for an astronomer.  What we especially like is spinning neutron stars: pulsars.  These emit radio beams out their north and south magnetic poles (no one is quite sure how).  If the neutron star’s rotation axis is not aligned with its magnetic axis (quite common in the Universe: even Earth’s are somewhat misaligned, which is why a magnetic compass doesn’t quite give true North), the radio beams sweep through a cone of space something like the beam from a lighthouse.  Every time one of the beams sweeps across earth, we see a flash (that is, a pulse) of radio emission.  Since nothing can speed up or slow down the rotation of a neutron star very quickly, the interval between pulses is exquisitely consistent for any given pulsar.  For a typical pulsar, this interval is a few seconds.

Consider what that means: an object twice the mass of our Sun is spinning several times a minute.

But even neutron stars like that have become comfortable, familiar objects in astronomy.  What Scott Ransom and his research group study are objects called millisecond pulsars, which rotate many times per second.  There is one – a neutron star more massive than the sun – that goes through 716 rotations every second.

These are really pretty fantastic objects.  As far as we can tell, they can only get spinning so fast by gravitationally devouring the outer layers of an orbiting companion star over a period of some millions of years.  The infalling gas from the companion star forms a rotating accretion disk that transfers angular momentum to the pulsar and makes it spin faster.  So millisecond pulsars are usually found close to (and in a binary orbit with) the dead core of a companion star whose outer layers they have eaten (this dead core is usually a kind of object called a white dwarf).  Ransom and other radio astronomers can measure the pulse times with exquisite accuracy – among the most accurate measurements in all of science – and use them to precisely calculate the orbit of the pulsar and its white dwarf companion.  In at least two cases they have seen an additional delay in the pulse times, which only happens when the pulsar is passing almost behind the white dwarf.  This delay is caused by the pulses taking longer to reach earth because they are traversing the curved space caused by the white dwarf’s gravity: a prediction of Einstein’s theory of General Relativity which has been precisely verified by observations of millisecond pulsars.

OK, millisecond pulsars are fine.  All the ones we know are in our own Milky Way Galaxy: they are too faint for us to see in other galaxies because of the huge intergalactic distances.  But Ransom had something to say about supermassive black holes in the centers of other galaxies.  Most galaxies apparently have one: our Milky Way’s is several million times the mass of the Sun.  It’s a wimp: some galaxies have a black hole tens of thousands of times bigger even than that.  So supermassive black holes are a normal part of galaxies.  Also, galaxies are colliding all the time (not to worry: the collisions take hundreds of millions of years, are usually harmless to the galaxies’ constituent stars and planets, and our Milky Way isn’t due for one until it hits the Andromeda Galaxy about 5 billion years from now).  Anyway, a frequent result of a collision between two galaxies is that they both merge into one bigger galaxy.  If both galaxies had supermassive black holes (which they usually do, as far as we can tell), the two supermassive black holes will both sink into the center of the new, merged galaxy, and eventually they will collide and merge.  In the last few centuries before they merge, they will be orbiting each other in a tight inward spiral and emitting gravitational waves (as predicted by Einstein).

Such gravitational waves haven’t yet been directly observed (they are really hard to detect), and the idea that black holes collide in merged galaxies hasn’t been proven, it’s just quite likely based on what we do know.  But Scott Ransom and his colleagues have determined that (with very careful observations) it should be possible to detect the signature of passing gravitational waves by monitoring the timing deviations they should cause in millisecond pulsars.  Basically, the gravitational waves from the colliding black holes will periodically stretch and compress the space between Earth and the millisecond pulsar, causing tiny variations in exactly when the pulses reach us.

So, astronomers get together and what do they talk about?  How to detect colliding supermassive black holes in distant galaxies by measuring the mysterious pulses of spinning neutron stars.  Even though our work is hard and our wild ideas don’t always work, I feel enormously blessed just to be able to talk and dream about stuff like that.  Yes, science is fun.

Monday, October 21, 2013

Boating, the Humphrey Bogart way

There is a boat in my driveway, on a trailer.  Both are a little unusual, which is entirely my fault: I built the boat, and modified the trailer to fit it.  The boat is inelegantly constructed of plywood and 2x4s, held together with hundreds of drywall screws and sealed with two hundred dollars’ worth of spar urethane varnish.  Its propulsion system is two oars and one thirty-four year old astronomer.  It laughs at the wakes of ferryboats and ski-boats: it is so wide and high-sided that it won’t capsize or swamp in anything less than a major storm.  On the other hand, wind and tidal currents laugh at it.  It has a top speed of about 2 mph, when I’m rowing for all I’m worth.  It also leaks about one half-gallon per hour: a rate slow enough to be irrelevant as regards safety, but fast enough to be annoying as regards shoes, lunches, and other things one might want to keep dry.

Yesterday was the boat’s fourth voyage, and likely its last before winter.  I and my friend Mark took it out with my three oldest children, ages 9, 7, and 3 (my wife and our youngest wisely stayed home).  We fought our way up the harbor into the teeth of a 10-15 mph wind, until we came to a standstill with Mark and me both rowing as hard as we could.  Plan B was working our way along the harborside, very close to shore in the lee of the forest.  But it seems the forest doesn’t have any lee with the wind coming from that direction.  It was time for Plan C.

In the 1951 movie, The African Queen, Humphrey Bogart and Catherine Hepburn accomplish a heroic navigation of a treacherous jungle river, only to find themselves entangled in a pathless, reed-choked delta.  Having exhausted all other options, Bogart climbs overboard and tries to pull their boat (the African Queen, of course) through the reeds, wading up to his neck in the leech-infested marsh.

Thankfully, though Port Jefferson Harbor does have reeds, they apparently come without leeches.  However, if you are considering getting out of a boat to wade through the shallows towing it, you should remove your cell phone from your pocket some minutes before making the attempt, rather than not finding time to do so as the boat blows swiftly toward a dangerous-looking submerged projection in the shallow water.  I jumped out and saved the boat at the cost of the cell phone: the right decision in terms of relative value, but still an idiotically preventable loss.  Then I took the bow-rope and towed the boat for several hundred yards: very satisfying to defeat the ever-moving wind and water by wading with one’s feet on solid ground.  I did find that shallows, even those full of reeds, are not always as shallow as could be wished.  But the children loved riding over the reeds.

We turned out of the main harbor and into a long, curving inlet fed by a small creek.  I waded a little more, but soon both the wind and the tidal current dropped enough that our oars were useful again.  The inlet was idyllic.  A wide diversity of boats, none ostentatious, rested at their moorings.  Lovely homes backed up against the water, which in places was lined with tall reeds – very different from the grass I had pulled us through – waving elegant-looking tassels in the wind.  The sun was warm, and hawks high overhead showed off their effortless mastery of aerodynamics. 

We rowed up the creek until it would no longer accommodate the boat, at which point we were within a fifty yards of a main road and a deli legendary for the quality of its sandwiches.  I considered tying up the boat and having us all troop up to the deli for a snack, but then pictured how our shoes would look plastered with the mud of the creek bank.  We turned around and rowed back, with the wind and current now blessedly in our favor.  Nine-year old Petra bailed diligently with a cracked plastic cup from a years-ago dinner at the Olive Garden.  The shadows grew long and the red sunset-light caught the trees on the east side of the harbor.  Mark delighted the children with a fairy story, complete with hilarious voices for a pet dragon and an evil witch who met her demise by being irreversibly transformed into a frog.  Comfortably before nightfall, we loaded the boat onto the trailer, bailed her out a little more, and headed home.

Saturday, October 19, 2013

Watching for Morning

Watching for morning means many things.  It has different meanings for the astronomer at his telescope, the student or careerist pulling an all-nighter, the father awake with a newborn or a sick child, the hiker walking through the night, the man in the toils of exhausted depression holding onto defiant hope that at last the sky will clear and the sun shine again in his soul – and the Christian trusting in the Biblical promise of an ultimate dawn, closer with every passing year: the return of Jesus with the destruction and rebirth of all creation. 
Or it could mean a chap up before dawn who just likes to see a pretty sunrise.

Thursday evening I set my alarm for 4 AM, because I had a lot to do Friday.  I woke up sometime in the middle of the night and changed the alarm to 4:30.  When it went off, I wished I had changed it to 5, and lay in bed until 4:40 just to spite it.  But I don’t fall asleep easily once wakened.  I showered and ate, and started walking by 5:45.

It’s about five miles from home to the university where I work, as a postdoc in astronomy.  Most days I commute on foot in the morning, and then my wife picks me up in the evening.  That way it’s good exercise without being excessive, and we can get by with just one car. The walk takes an hour and a half.  I don’t usually leave before dawn, so Friday morning was special.

There was a beautiful full moon ahead of me as I walked, beginning to look orange as it lowered over the trees.  It’s autumn in New York, but the biting cold hasn’t yet arrived: the air was pleasant to walk through.  Sirius and Jupiter shone overhead: of all star-like objects in our sky, only Venus – or a galactic supernova – can be brighter.

Though stressed, driven, and weary, I was happy for no reason.  The sight of the full moon over the trees made me think of the skyline drive at dusk near Shenandoah, years ago when I was a child.  A moon like that – only huger and more orange – rose low over the hills as I watched out the back-seat windows of our car.  We passed dozens of deer – not threatening to cross the road, only feeding under the eaves of the forest.  My parents were astonished at their numbers.  The hills, the moon, the deer, and the excitement of being on vacation – far from home and yet safe at the same time – combined to make the drive magical in all the best and deepest senses of the word.

I don’t experience things that way any more as an adult.  I have to know too much now, and there’s less space for wonder.  Now I have to be one of the responsible parents in the front seat, figuring out where we are going to eat and sleep, and how much gas we have left.

There are compensations.  I’ve been blessed with the opportunity to do many of the things I only daydreamed about as a child.  The job I’m walking to – a job as a professional astronomer, however modestly paid – is one of those impossible dreams come true.  Even when I’m hanging on, as Rich Mullins sings, “somewhere… between the passion and fatigue,” I know astronomy is one of the things I was born to do.

I pause, leaning over a low wooden fence in the brightening dawn.  Trees at the other side of a field, partly bare now with the autumn, stand silhouetted against the pale blue light in the sky.  The moon is gone; I can’t remember when I lost sight of it.  Far overhead, more distant and perfect than it ever appears in the night sky, Jupiter is fading in the growing light.  For a moment I remember how small I am, and there is peace in the thought.  This beauty – from the earthly dawn to the unimaginable distances of the cosmos – means something immeasurably important.  Yes, my thoughts and feelings are, at some level, neurological electrochemistry.  Yet if there is any meaning at all in my electrochemistry, it constrains me to believe that the beauty of the Universe is more than a flicker of pleasure in the hominid brain.  It is the splendid artistry of God, in which the Creator himself delights.  It stands, regardless of my dreams and my fears – regardless of which, if either, are fulfilled.  It does not matter that I am tired and stressed, that my future is uncertain and I have so much to lose.  The beauty and the glory stand, nothing that I fear can even touch them, and they are what matters.

The moment passes quickly, and I am my anxious self again.  But something of the peace remains.