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I participated in an experts’ roundtable for Aeon Magazine, in which we were asked (more or less facetiously) what single project we would support to settle either questions about the very early universe or the existence of life elsewhere in the cosmos. Of course my real answer is that we should support all the science, because discovery isn’t about looking for one thing, but seeing what new things we can find. Throwing all our money at one big project might accomplish something, but it’s a bad way to do science. But anyway, taking the question for what it is — a fun exercise in wishing — here’s my answer, along with thoughts from Ross Andersen and Caleb Scharf.
The BICEP2 telescope (foreground) with the South Pole Telescope (SPT) behind. [Credit: Steffen Richter (Harvard University)]
Today was an exciting and stimulating day: the BICEP2 collaboration announced the first measurement of the cosmic microwave background that might tell us whether or not inflation happened. Inflation is the hypothetical rapid expansion of the Universe during its first instants, which explains a lot about why the cosmos appears the way it does. However, data on inflation itself, as opposed to its side-effects, are hard to come by. This new observation could help resolve that
…assuming we can figure out why some of its aspects don’t agree with prior observations.
While they do not constitute a direct detection of either primordial gravitational waves (the distortions causing the light polarization) or inflation, the BICEP2 results could provide the best evidence for both that could not be easily explained away by other theories. This observation cannot be the end of the story, however. The measurement of polarization is significantly larger that what is seen in the results of prior observations in a way that cannot be immediately dismissed. Whether the problems are with the interpretation and analysis of the BICEP2 data, or if something more subtle is at work, remains to be seen. [Read more….]
X-ray image of two black holes in the galaxy NGC 6240. Binary systems like this are possibly the origin of the most massive black holes in the cosmos. [Credit: NASA/CXC/MPE/S.Komossa et al.]
The most massive known object in the cosmos is the black hole at the center of M87, a huge galaxy in the Virgo Cluster. While most large galaxies (including the Milky Way) harbor supermassive black holes, the very largest are interesting. That’s because galaxies and their black holes seem to share a history, based on the relationship between the mass of the black hole and the mass of the galaxy’s central region. Since large galaxies grew by devouring smaller galaxies, or by two galaxies merging into a larger one, it’s very likely the biggest black holes followed a similar process. My latest piece for Nautilus examines how this process might have taken place,
and what it could reveal about the black holes themselves.
Earth emits gravitational waves as it orbits the Sun, though the amount of energy lost is imperceptible over the lifetime of the Solar System. Binary black holes are a different matter: Once they are relatively close, they shed a tremendous amount of energy, bringing them closer together with each orbit. (Binary black stars are thought to emit more gravitational energy as they merge than regular stars emit in the form of UV, IR, and visible light over their entire lifetimes of billions of years.) Eventually their event horizons will touch, and the system emits a lot more gravitational waves in a phase known as “ring-down,” as the lumpy, uneven merged mass becomes a smooth, perfectly symmetrical black hole. [Read more…]
I’m at GeekGirlCon this weekend, so I’m busy with non-writing activities as part of the DIY Science Zone. Thanks to our Fearless Leader Dr. “Nick Fury” Rubidium for putting our part of the event together!
- Where Nature Hides the Darkest Mystery of All (Nautilus): Even though there’s no solid barrier, the event horizon of a black hole provides a boundary through which we can’t see or probe. That leads to a troubling idea: will we ever know what’s really inside that event horizon? Is there any way to learn about the interior by indirect measurements?
- Black hole hair and the dark energy problem (Galileo’s Pendulum): Building off that article, what happens if our standard theory of gravity is modified? That’s not an entirely crazy idea: several modifications to general relativity have been proposed, inspired by inflation (the rapid expansion during the cosmos’ earliest moments) or dark energy. A recent paper examined that idea, and here’s my take.
- Strongly magnetic pulsar could explain anomalous supernovas (Ars Technica): Some supernovas are particularly bright, especially some from the early Universe. These, known as “pair-instability” supernovas, are the explosion of very massive stars made of nearly pure hydrogen and helium. However, some of these super-luminous supernovas don’t quite fit that profile, including being too close. A new set of observations may show they are actually driven by a magnetar, a highly magnetized pulsar.
- Gravitational waves show deficit in black hole collisions (Ars Technica): Mergers of supermassive black holes should happen frequently enough to produce a bath of gravitational radiation permeating the cosmos. While that gravitational wave background (GWB) possesses wavelengths too large for ground-based detectors like LIGO, astronomers realized it might be visible in the fluctuations of light from pulsars. However, they didn’t see what they expected, leading to the big question: why not?
The general theory of relativity is the reigning champion of gravitational theories: it’s withstood tests in the Solar System, near black holes, and in binary systems. Most recently, astronomers performed detailed observations of a pulsar-white dwarf binary system, which provided an exquisite example of general relativity in action. Pulsars and white dwarfs are both the remnants of stars, but pulsars in particular are interesting: they pack the mass of a star into a sphere about 20 kilometers across. That means the gravity at the surface of a pulsar is extreme, so when one is in a binary system, it provides a laboratory for measuring strong gravitational effects.
The pulsar itself was interesting because of its relatively high mass: about 2.0 times that of the Sun (most observed pulsars are about 1.4 times more massive). Unlike more mundane objects, pulsar size doesn’t grow with mass; according to some models, a higher mass pulsar may actually be smaller than one with lower mass. As a result, the gravity at the surface of PSR J0348+0432 is far more intense than at a lower-mass counterpart, providing a laboratory for testing general relativity (GR). The gravitational intensity near PSR J0348+0432 is about twice that of other pulsars in binary systems, creating a more extreme environment than previously measured. [Read more…]
Also, let the record show: it’s possible to write an article about testing general relativity without mentioning Einstein, much less making the story about “proving him right” (or wrong).
My second piece for BBC Future is up! I ask—and partly answer—the question, “Will we ever detect gravitational waves directly?” (And don’t worry if you don’t know what a gravitational wave is: I answer that one too!)
A major part of the problem is that gravity is weak: even the strongest gravitational wave will only nudge an atom by a tiny amount. Additionally, the wavelength of gravitational radiation – the distance over which a wave repeats itself – is often similar to the size of the objects emitting it. So, while radio waves from pulsars may have wavelengths measured in centimetres, the gravitational radiation emitted could have wavelengths measured in kilometres. Which means that you most likely need detectors of a similar size to detect them. [Read more…]
For those of you in the UK, you might need to use this link instead, due to weird issues with the BBC website.