Tag Archives: astronomy

Giving two free lectures 6/20,27 about gravitational waves

For those of you who live in or around Berkshire County, Massachusetts, or know people who do…

Starting next week I’ll be giving two free lectures about the LIGO experiment’s discovery of gravitational waves.  The lectures will be at 1:30 pm on Mondays June 20 and 27, at Berkshire Community College in Pittsfield, MA.  The first lecture will focus on why gravitational waves were expected by scientists, and the second will be on how gravitational waves were discovered, indirectly and then directly.  No math or science background will be assumed.  (These lectures will be similar in style to the ones I gave a couple of years ago concerning the Higgs boson discovery.)

Here’s a flyer with the details:  http://berkshireolli.org/ProfessorMattStrasslerOLLILecturesFlyer.pdf

Advance Thoughts on LIGO

Scarcely a hundred years after Einstein revealed the equations for his theory of gravity (“General Relativity”) on November 25th, 1915, the world today awaits an announcement from the LIGO experiment, where the G in LIGO stands for Gravity. (The full acronym stands for “Laser Interferometer Gravitational Wave Observatory.”) As you’ve surely heard, the widely reported rumors are that at some point in the last few months, LIGO, recently upgraded to its “Advanced” version, finally observed gravitational waves — ripples in the fabric of space (more accurately, of space-time). These waves, which can make the length of LIGO shorter and longer by an incredibly tiny amount, seem to have come from the violent merger of two black holes, each with a mass [rest-mass!] dozens of times larger than the Sun. Their coalescence occurred long long ago (billions of years) in a galaxy far far away (a good fraction of the distance across the visible part of the universe), but the ripples from the event arrived at Earth just weeks ago. For a brief moment, it is rumored, they shook LIGO hard enough to be convincingly observed.

For today’s purposes, let me assume the rumors are true, and let me assume also that the result to be announced is actually correct. We’ll learn today whether the first assumption is right, but the second assumption may not be certain for some months (remember OPERA’s [NOT] faster-than-light neutrinos  and BICEP2’s [PROBABLY NOT] gravitational waves from inflation). We must always keep in mind that any extraordinary scientific result has to be scrutinized and confirmed by experts before scientists will believe it! Discovery is difficult, and a large fraction of such claims — large — fail the test of time.

What the Big News Isn’t

There will be so much press and so many blog articles about this subject that I’m just going to point out a few things that I suspect most articles will miss, especially those in the press.

Most importantly, if LIGO has indeed directly discovered gravitational waves, that’s exciting of course. But it’s by no means the most important story here.

That’s because gravitational waves were already observed indirectly, quite some time ago, in a system of two neutron stars orbiting each other. This pair of neutron stars, discovered by Joe Taylor and his graduate student Russell Hulse, is interesting because one of the neutron stars is a pulsar, an object whose rotation and strong magnetic field combine to make it a natural lighthouse, or more accurately a radiohouse, sending out pulses of radio waves that can be detected at great distances. The time between pulses shifts very slightly as the pulsar moves toward and away from Earth, so the pulsar’s motion around its companion can be carefully monitored. Its orbital period has slowly changed over the decades, and the changes are perfectly consistent with what one would expect if the system were losing energy, emitting it in the form of unseen gravitational waves at just the rate predicted by Einstein’s theory (as shown in this graph.) For their discovery, Hulse and Taylor received the 1993 Nobel Prize. By now, there are other examples of similar pairs of neutron stars, also showing the same type of energy loss in detailed accord with Einstein’s equations.

A bit more subtle (so you can skip this paragraph if you want), but also more general, is that some kind of gravitational waves are inevitable… inevitable, after you accept Einstein’s earlier (1905) equations of special relativity, in which he suggested that the speed of light is a sort of universal speed limit on everything, imposed by the structure of space-time.  Sound waves, for instance, exist because the speed of sound is finite; if it were infinite, a vibrating guitar string would make the whole atmosphere wiggle back and forth in sync with the guitar string.  Similarly, since effects of gravity must travel at a finite speed, the gravitational effects of orbiting objects must create waves. The only question is the specific properties those waves might have.

No one, therefore, should be surprised that gravitational waves exist, or that they travel at the universal speed limit, just like electromagnetic waves (including visible light, radio waves, etc.) No one should even be surprised that the waves LIGO is (perhaps) detecting have properties predicted by Einstein’s specific equations for gravity; if they were different in a dramatic way, the Hulse-Taylor neutron stars would have behaved differently than expected.

Furthermore, no one should be surprised if waves from a black hole merger have been observed by the Advanced LIGO experiment. This experiment was designed from the beginning, decades ago, so that it could hardly fail to discover gravitational waves from the coalescence of two black holes, two neutron stars, or one of each. We know these mergers happen, and the experts were very confident that Advanced LIGO could find them. The really serious questions were: (a) would Advanced LIGO work as advertised? (b) if it worked, how soon would it make its first discovery? and (c) would the discovery agree in detail with expectations from Einstein’s equations?

Big News In Scientific Technology

So the first big story is that Advanced LIGO WORKS! This experiment represents one of the greatest technological achievements in human history. Congratulations are due to the designers, builders, and operators of this experiment — and to the National Science Foundation of the United States, which is LIGO’s largest funding source. U.S. taxpayers, who on average each contributed a few cents per year over the past two-plus decades, can be proud. And because of the new engineering and technology that were required to make Advanced LIGO functional, I suspect that, over the long run, taxpayers will get a positive financial return on their investment. That’s in addition of course to a vast scientific return.

Advanced LIGO is not even in its final form; further improvements are in the works. Currently, Advanced LIGO consists of two detectors located 2000 miles (3000 kilometers) apart. Each detector consists of two “arms” a few miles (kilometers) long, oriented at right angles, and the lengths of the arms are continuously compared.  This is done using exceptionally stable lasers reflecting off exceptionally perfect mirrors, and requiring use of sophisticated tricks for mitigating all sorts of normal vibrations and even effects of quantum “jitter” from the Heisenberg uncertainty principle. With these tools, Advanced LIGO can detect when passing gravitational waves change the lengths of LIGO’s arms by … incredibly … less than one part in a billion trillion (1,000,000,000,000,000,000,000). That’s an astoundingly tiny distance: a thousand times smaller than the radius of a proton. (A proton itself is a hundred thousand times smaller, in radius, than an atom. Indeed, LIGO is measuring a distance as small as can be probed by the Large Hadron Collider — albeit with a very very tiny energy, in contrast to the collider.) By any measure, the gravitational experimenters have done something absolutely extraordinary.

Big News In Gravity

The second big story: from the gravitational waves that LIGO has perhaps seen, we would learn that the merger of two black holes occurs, to a large extent, as Einstein’s theory predicts. The success of this prediction for what the pattern of gravitational waves should be is a far more powerful test of Einstein’s equations than the mere existence of the gravitational waves!

Imagine, if you can… Two city-sized black holes, each with a mass [rest-mass!] tens of times greater than the Sun, and separated by a few tens of miles (tens of kilometers), orbit each other. They circle faster and faster, as often, in their last few seconds, as 100 times per second. They move at a speed that approaches the universal speed limit. This extreme motion creates an ever larger and increasingly rapid vibration in space-time, generating large space-time waves that rush outward into space. Finally the two black holes spiral toward each other, meet, and join together to make a single black hole, larger than the first two and spinning at an incredible rate.  It takes a short moment to settle down to its final form, emitting still more gravitational waves.

During this whole process, the total amount of energy emitted in the vibrations of space-time is a few times larger than you’d get if you could take the entire Sun and (magically) extract all of the energy stored in its rest-mass (E=mc²). This is an immense amount of energy, significantly more than emitted in a typical supernova. Indeed, LIGO’s black hole merger may perhaps be the most titanic event ever detected by humans!

This violent dance of darkness involves very strong and complicated warping of space and time. In fact, it wasn’t until 2005 or so that the full calculation of the process, including the actual moment of coalescence, was possible, using highly advanced mathematical techniques and powerful supercomputers!

By contrast, the resulting ripples we get to observe, billions of years later, are much more tame. Traveling far across the cosmos, they have spread out and weakened. Today they create extremely small and rather simple wiggles in space and time. You can learn how to calculate their properties in an advanced university textbook on Einstein’s gravity equations. Not for the faint of heart, but certainly no supercomputers required.

So gravitational waves are the (relatively) easy part. It’s the prediction of the merger’s properties that was the really big challenge, and its success would represent a remarkable achievement by gravitational theorists. And it would provide powerful new tests of whether Einstein’s equations are in any way incomplete in their description of gravity, black holes, space and time.

Big News in Astronomy

The third big story: If today’s rumor is indeed of a real discovery, we are witnessing the birth of an entirely new field of science: gravitational-wave astronomy. This type of astronomy is complementary to the many other methods we have of “looking” at the universe. What’s great about gravitational wave astronomy is that although dramatic events can occur in the universe without leaving a signal visible to the eye, and even without creating any electromagnetic waves at all, nothing violent can happen in the universe without making waves in space-time. Every object creates gravity, through the curvature of space-time, and every object feels gravity too. You can try to hide in the shadows, but there’s no hiding from gravity.

Advanced LIGO may have been rather lucky to observe a two-black-hole merger so early in its life. But we can be optimistic that the early discovery means that black hole mergers will be observed as often as several times a year even with the current version of Advanced LIGO, which will be further improved over the next few years. This in turn would imply that gravitational wave astronomy will soon be a very rich subject, with lots and lots of interesting data to come, even within 2016. We will look back on today as just the beginning.

Although the rumored discovery is of something expected — experts were pretty certain that mergers of black holes of this size happen on a fairly regular basis — gravitational wave astronomy might soon show us something completely unanticipated. Perhaps it will teach us surprising facts about the numbers or properties of black holes, neutron stars, or other massive objects. Perhaps it will help us solve some existing mysteries, such as those of gamma-ray bursts. Or perhaps it will reveal currently unsuspected cataclysmic events that may have occurred somewhere in our universe’s past.

Prizes On Order?

So it’s really not the gravitational waves themselves that we should celebrate, although I suspect that’s what the press will focus on. Scientists already knew that these waves exist, just as they were aware of the existence of atoms, neutrinos, and top quarks long before these objects were directly observed. The historic aspects of today’s announcement would be in the successful operation of Advanced LIGO, in its new way of “seeing” the universe that allows us to observe two black holes becoming one, and in the ability of Einstein’s gravitational equations to predict the complexities of such an astronomical convulsion.

Of course all of this is under the assumptions that the rumors are true, and also that LIGO’s results are confirmed by further observations. Let’s hope that any claims of discovery survive the careful and proper scrutiny to which they will now be subjected. If so, then prizes of the highest level are clearly in store, and will be doled out to quite a few people, experimenters for designing and building LIGO and theorists for predicting what black-hole mergers would look like. As always, though, the only prize that really matters is given by Nature… and the many scientists and engineers who have contributed to Advanced LIGO may have already won.

Enjoy the press conference this morning. I, ironically, will be in the most inaccessible of places: over the Atlantic Ocean.  I was invited to speak at a workshop on Large Hadron Collider physics this week, and I’ll just be flying home. I suppose I can wait 12 hours to find out the news… it’s been 44 years since LIGO was proposed…

How Evidence for Cosmic Inflation Was Reduced to Dust

Many of you will have read in the last week that unfortunately (though to no one’s surprise after seeing the data from the Planck satellite in the last few months) the BICEP2 experiment’s claim of a discovery of gravitational waves from cosmic inflation has blown away in the interstellar wind. [For my previous posts on BICEP2, including a great deal of background information, click here.] The BICEP2 scientists and the Planck satellite scientists have worked together to come to this conclusion, and written a joint paper on the subject.  Their conclusion is that the potentially exciting effect that BICEP2 observed (“B-mode polarization of the cosmic microwave background on large scales”; these terms are explained here) was due, completely or in large part, to polarized dust in our galaxy (the Milky Way). The story of how they came to this conclusion is interesting, and my goal today is to explain it to non-experts.  Click here to read more.

How Far We Have Come(t)

It wasn’t that long ago, especially by cometary standards, that humans viewed the unpredictable and spectacular arrival of a comet, its tail spread across the sky unlike any star or planet, as an obviously unnatural event. How could an object flying so dramatically and briefly through the heavens be anything other than a message from a divine force? Even a few hundred years ago…

Today a human-engineered spacecraft descended out of the starry blackness and touched one.

We have known for quite some time that our ancestors widely maligned these icy rocks, often thinking them messengers of death and destruction.  Yes, a comet is, at some level, not much more than an icy rock. Yet, heated by the sun, it can create one of our sky’s most bewitching spectacles. Actually two, because not only can a comet itself be a fabulous sight, the dust it leaves behind can give us meteor showers for many years afterward.

But it doesn’t stop there.  For comets, believed to be frozen relics of the ancient past, born in the early days of the Sun and its planets, may have in fact been messengers not of death but of life.   When they pummeled our poor planet in its early years, far more often than they do today, their blows may have delivered the water for the Earth’s oceans and the chemical building blocks for its biology.   They may also hold secrets to understanding the Earth’s history, and perhaps insights into the more general questions of what happens when stars and their planets form.  Indeed, as scientific exploration of these objects moves forward, they may teach us the answers to questions that we have not yet even thought to ask.

Will the Philae lander maintain its perch or lose its grip? Will it function as long as hoped? No matter what, today’s landing was as momentous as the first spacecraft touchdowns on the Moon, Venus, Mars, Titan (Saturn’s largest moon), and a small asteroid — and also, the first descent of a spacecraft into Jupiter’s atmosphere. Congratulations to those who worked so hard and so long to get this far! Now let’s all hope that they, and their spacecraft, can hang on a little longer.

Auroras — Quantum Physics in the Sky — Tonight?

Maybe. If we collectively, and you personally, are lucky, then maybe you might see auroras — quantum physics in the sky — tonight.

Before I tell you about the science, I’m going to tell you where to get accurate information, and where not to get it; and then I’m going to give you a rough idea of what auroras are. It will be rough because it’s complicated and it would take more time than I have today, and it also will be rough because auroras are still only partly understood.

Bad Information

First though — as usual, do NOT get your information from the mainstream media, or even the media that ought to be scientifically literate but isn’t. I’ve seen a ton of misinformation already about timing, location, and where to look. For instance, here’s a map from AccuWeather, telling you who is likely to be able to see the auroras.

Don't believe this map by AccuWeather.  Oh, sure, they know something about clouds.  But auroras, not much.

Don’t believe this map by AccuWeather. Oh, sure, they know something about clouds. But auroras, not much.

See that line below which it says “not visible”? This implies that there’s a nice sharp geographical line between those who can’t possibly see it and those who will definitely see it if the sky is clear. Nothing could be further than the truth. No one knows where that line will lie tonight, and besides, it won’t be a nice smooth curve. There could be auroras visible in New Mexico, and none in Maine… not because it’s cloudy, but because the start time of the aurora can’t be predicted, and because its strength and location will change over time. If you’re north of that line, you may see nothing, and if you’re south of it you still might see something.  (Accuweather also says that you’ll see it first in the northeast and then in the midwest.  Not necessarily.  It may become visible across the U.S. all at the same time.  Or it may be seen out west but not in the east, or vice versa.)

Auroras aren’t like solar or lunar eclipses, absolutely predictable as to when they’ll happen and who can see them. They aren’t even like comets, which behave unpredictably but at least have predictable orbits. (Remember Comet ISON? It arrived exactly when expected, but evaporated and disintegrated under the Sun’s intense stare.) Auroras are more like weather — and predictions of auroras are more like predictions of rain, only in some ways worse. An aurora is a dynamic, ever-changing phenomenon, and to predict where and when it can be seen is not much more than educated guesswork. No prediction of an aurora sighting is EVER a guarantee. Nor is the absence of an aurora prediction a guarantee one can’t be seen; occasionally they appear unexpectedly.  That said, the best chance of seeing one further away from the poles than usual is a couple of days after a major solar flare — and we had one a couple of days ago.

Good Information and How to Use it

If you want accurate information about auroras, you want to get it from the Space Weather Prediction Center, click here for their main webpage. Look at the colorful graph on the lower left of that webpage, the “Satellite Environment Plot”. Here’s an example of that plot taken from earlier today:

The "Satellite Environment Plot" from earlier today; focus your attention on the two lower charts, the one with the red and blue wiggly lines (GOES Hp) and on the one with the bars (Kp Index).  How to use them is explained in the text.

The “Satellite Environment Plot” from earlier today; focus your attention on the two lower charts, the one with the red and blue wiggly lines (GOES Hp) and on the one with the bars (Kp Index). How to use them is explained in the text.

There’s a LOT of data on that plot, but for lack of time let me cut to the chase. The most important information is on the bottom two charts. Continue reading

BICEP2’s Cosmic Polarization: Published, Reduced in Strength

I’m busy dealing with the challenges of being in a quantum superposition, but you’ve probably heard: BICEP2’s paper is now published, with some of its implicit and explicit claims watered down after external and internal review. The bottom line is as I discussed a few weeks ago when I described the criticism of the interpretation of their work (see also here).

  • There is relatively little doubt (but it still requires confirmation by another experiment!) that BICEP2 has observed interesting polarization of the cosmic microwave background (specifically: B-mode polarization that is not from gravitational lensing of E-mode polarization; see here for more about what BICEP2 measured)
  • But no one, including BICEP2, can say for sure whether it is due to ancient gravitational waves from cosmic inflation, or to polarized dust in the galaxy, or to a mix of the two; and the BICEP2 folks are explicitly less certain about this, in the current version of their paper, than in their original implicit and explicit statements.

And we won’t know whether it’s all just dust until there’s more data, which should start to show up in coming months, from BICEP2 itself, from Planck, and from other sources. However, be warned: the measurements of the very faint dust that might be present in BICEP2’s region of the sky are extremely difficult, and the new data might not be immediately convincing. To come to a consensus might take a few years rather than a few months.  Be patient; the process of science, being self-correcting, will eventually get it straight, but not if you rush it.

Sorry I haven’t time to say more right now.

The BICEP2 Dust-Up Continues

The controversy continues to develop over the interpretation of the results from BICEP2, the experiment that detected “B-mode” polarization in the sky, and was hailed as potential evidence of gravitational waves from the early universe, presumably generated during cosmic inflation. [Here’s some background info about the measurement].

Two papers this week (here and here) gave more detailed voice to the opinion that the BICEP2 team may have systematically underestimated the possible impact of polarized dust on their measurement.  These papers raise (but cannot settle) the question as to whether the B-mode polarization seen by BICEP2 might be entirely due to this dust — dust which is found throughout our galaxy, but is rather tenuous in the direction of the sky in which BICEP2 was looking.

I’m not going to drag my readers into the mud of the current discussion, both because it’s very technical and because it’s rather vague and highly speculative. Even the authors of the two papers admit they leave the situation completely unsettled.  But to summarize, the main purpose and effect of these papers seems to be this:

Continue reading

A Bright Flash in the Neighborhood

NOTE ADDED: FALSE ALARM!  DISREGARD! HERE’S SWIFT’S DETAILED EXPLANATION AS TO WHY! with my own brief summary below.

Comparable in size to the Milky Way, our host galaxy, the Andromeda galaxy is the most distant object easily visible (in dark skies) to the naked eye; it lies 2.5 million light-years away.  About 2.5 million years ago, something in this distant star city went “boom”.  And in doing so it flashed, brightly, in high-energy photons — particles of light (or, more precisely, particles of electromagnetic radiation, of which visible light is just an example) — photons that carry many thousands of times more energy than do the photons that our eyes are designed to see.

File:Andromeda Galaxy (with h-alpha).jpg

The Andromeda Galaxy (photo from Creative Commons), which contains perhaps 100 billion stars or more. Something in here exploded a while back, and we just found out about it.

Some of these photons, after traveling for millions of years across space, arrived at Earth this afternoon.  They showed up in the Swift satellite’s telescopes, which are designed precisely to notice these things.  And Swift’s telescopes identified these photons as arriving from a location somewhere within Andromeda… within a globular cluster of stars, a tightly-knit neighborhood within the city that is Andromeda.  NOTE ADDED: Actually, a combination of low-probability events caused

  • a false alarm, of a sort that’s rare but not unexpected: a known object in Andromeda that emits X-rays appeared to brighten, as a result of electronic noise in Swift’s instruments (such noise is always present, in all scientific instruments, and it is normal to occasionally get a strong burst of it)
  • followed (due perhaps to a poorly-timed computer problem at Swift’s data center, which slowed the arrival of more complete information the Swift people know why but haven’t explained it in detail) by a delay in identifying this apparent brightening as a false alarm;

all of which is explained here.  The apparent brightening, which was rather mild, would in fact have been completely disregarded if it hadn’t occurred in Andromeda; for relatively nearby objects like Andromeda, the Swift team sets a low threshold for false alarms, because something real would be so amazingly important and exciting that we can’t afford to miss it. 

What caused this colossal explosion, perhaps the nearest of its type ever observed by modern astronomers?  That is the burning question that astronomers, and their friends in gravitational physics and particle physics, are aching to know.  It is likely that by tomorrow morning, and certainly within the next couple of days, we’ll know much more… perhaps we’ll even learn something of great importance.  NOTE ADDED: And indeed, we know.

For the moment, though, there’s lots of guessing, most all of which will turned out to be wrong.  (Maybe, some are speculating, this is a gamma-ray burst, perhaps caused by a merger of two neutron stars, with consequent bursts of neutrinos and gravitational waves that we might detect; but right now there’s no evidence for this, so don’t get your hopes up.)  You can read many breathless articles by following the Twitter hashtag #GRBm31.  Admittedly you might be better off without it.  NOTE ADDED: Yep.

But do stay tuned as the facts emerge.  The opportunity to observe such a nearby explosion is rare.  So this is certainly going to be interesting… and maybe, if we’re very lucky, it will be more than merely interesting…

NOTE ADDED: Actually, we were very unlucky, and it was completely uninteresting —except as an illustration that it can be very difficult, in the heat of a moment when data is sparse, to distinguish between something scientifically fascinating and a weird fluke.  Scientists do expect these things to happen sometimes.  Fortunately, science is self-correcting.  Even if Swift’s team hadn’t identified this signal as a fluke in their data, other telescopes would have been unable to find the object they’d identified, and doubts would quickly have emerged as a result.  If something’s real, everyone will see it.  

The lesson, in my view, is that when new scientific results are announced, be patient.  Give the experts a little time to check things, and don’t do science the way Twitter does.

And finally: if you are inclined to criticize the Swift team, you’re making a big mistake.  On the contrary, they did exactly what they were supposed to do, as quickly as they could.  Gamma-ray bursts [GRBs] are extremely rare and extremely valuable and extremely brief; Swift’s job is to let the scientific community know, as quickly as possible, that one may have been seen, so that others may look at it.  Inevitably, someone with such a job will occasionally give a false alarm.  Swift has discovered so many GRB’s, and made so many direct and indirect contributions to our knowledge about them and about other objects in the sky, that scientists, while disappointed that this was a false alarm, will certainly not view Swift as irresponsible.  

A week ago, regarding BICEP2’s results coming into question, Seth Zenz wrote a nice, short article on Why, in Science, it’s OK to be Wrong.  I recommend it.