Seeing the invisible monster at the Milky Way center

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This is my second print magazine feature for Smithsonian Air & Space Magazine. The first was about gravitational waves, published not long before the LIGO detector found the first gravitational wave signals. The new piece is about the black hole at the center of our galaxy, published just a few months before…well, read the article to see why this is a good time to be writing about that particular black hole.

The First Sighting of a Black Hole

We know one lurks at the center of the Milky Way, but to these astronomers, seeing will be believing

For Smithsonian Air & Space Magazine:

he center of the galaxy doesn’t look like much, even if you’re lucky enough to live in a place where the night sky is sufficiently dark to see the bands of the Milky Way. In visible light, the stars between here and there blur together into a single brilliant source, like a bright beam hiding the lighthouse behind it.

But in other types of radiation—radio waves, infrared, X-rays—astronomers have detected the presence of an object with the mass of four million suns packed into a region smaller than our solar system: a supermassive black hole.

Astronomers call it Sagittarius A*, or Sgr A* (pronounced “sadge A star”) for short, because it’s located (from our point of view) in the Sagittarius constellation. Discovering the Milky Way’s black hole has helped cement the idea that the center of nearly every large galaxy harbors a supermassive black hole. But despite mounting evidence for black holes, we still haven’t seen one directly. [Read the rest at Smithsonian Air & Space Magazine]

A discovery that made a thousand scientists burst into cheers and tears

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Part of one of the mirror assemblies that make up the Laser Interferometer Gravitational-wave Observatory (LIGO) at Livingston, Louisiana. I visited the site in 2012 during the upgrade of the lab to Advanced LIGO. [Credit: moi]

Part of one of the mirror assemblies that make up the Laser Interferometer Gravitational-wave Observatory (LIGO) at Livingston, Louisiana. I visited the site in 2012 during the upgrade of the lab to Advanced LIGO. [Credit: moi]

It’s not every day that we get to usher in an entirely new branch of astronomy. Yesterday, members of the LIGO collaboration announced the first direct detection of gravitational waves, which are a way to study the universe we can’t see using light. Much of my PhD research involved gravitational physics, including a bit of gravitational wave work. I even visited LIGO twice because … well, why not? For that reason, yesterday’s announcement brought tears to my eyes, and I’m not the only one. This is the start of a new in the study of the universe. And here’s what I had to say about it for The Atlantic:

The Dawn of a New Era in Science

By announcing the first detection of gravitational waves, scientists have vindicated Einstein and given humans a new way to look at the universe

For The Atlantic:

More than a billion years ago, in a galaxy that sits more than a billion light-years away, two black holes spiraled together and collided. We can’t see this collision, but we know it happened because, as Albert Einstein predicted a century ago, gravitational waves rippled out from it and traveled across the universe to an ultra-sensitive detector here on Earth.

This discovery, announced today by researchers with the Laser Interferometer Gravitational-wave Observatory (LIGO), marks another triumph for Einstein’s general theory of relativity. And more importantly, it marks the beginning of a new era in the study of the universe: the advent of gravitational-wave astronomy. The universe has just become a much more interesting place. [Read the rest at The Atlantic]

How can we see black holes if they’re invisible?

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The Shadow of a Black Hole

From NOVA:

The invisible manifests itself through the visible: so say many of the great works of philosophy, poetry, and religion. It’s also true in physics: we can’t see atoms or electrons directly and dark matter seems to be entirely transparent, yet this invisible stuff makes and shapes the universe as we know it.

Then there are black holes: though they are the most extreme gravitational powerhouses in the cosmos, they are invisible to our telescopes. Black holes are the unseen hand steering the evolution of galaxies, sometimes encouraging new star formation, sometimes throttling it. The material they send jetting away changes the chemistry of entire galaxies. When they take the form of quasars and blazars, black holes are some of the brightest single objects in the universe, visible billions of light-years away. The biggest supermassive black holes are billions of times as massive as the Sun. They are engines of creation and destruction that put the known laws of physics to their most extreme test. Yet, we can’t actually see them. [read the rest at NOVA…]

This piece, which emphasizes the great science coming from the Event Horizon Telescope (EHT), is a  companion to my earlier NOVA essay, “Do we need to rewrite general relativity?”

Listening to the sounds of the cosmos

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Last year, I went to a conference in Florida to hear — and in some cases meet — some of the leading thinkers in the study of gravitational waves. These waves are disturbances in the structure of spacetime itself, and could provide information about some exciting phenomena, if we can learn to detect them. The universe as heard in gravitational waves includes colliding black holes, white dwarfs locked in mutual orbits, exploding stars, and possibly chaotic disturbances from the very first instants after the Big Bang. This story marks one of my first big magazine articles, which I wrote for Smithsonian Air & Space magazine.

The Universe is Ringing

And astronomers are building observatories to listen to it

For Smithsonian Air & Space:

Think of it as a low hum, a rumble too deep to notice without special equipment. It permeates everything—from the emptiest spot in space to the densest cores of planets. Unlike sound, which requires air or some other material to carry it, this hum travels on the structure of space-time itself. It is the tremble caused by gravitational radiation, left over from the first moments after the Big Bang.

Gravitational waves were predicted in Albert Einstein’s 1916 theory of general relativity. Einstein postulated that the gravity of massive objects would bend or warp space-time and that their movements would send ripples through it, just as a ship moving through water creates a wake. Later observations supported his conception. [Read the rest at Air & Space….]

This metal plate is perforated with holes, each of which lines up with a galaxy or quasar. The BOSS survey maps the position and distance to a huge number of galaxies using many masks such as this. [Credit: moi]

This metal plate is perforated with holes, each of which lines up with a galaxy or quasar. The BOSS survey maps the position and distance to a huge number of galaxies using many masks such as this. [Credit: moi]

Far from being invisible, black holes are among some of the brightest objects in the Universe. The black holes themselves aren’t emitting light, but the matter they draw in heats up and much of it shoots back out in powerful jets. When that happens, the black hole is known as a quasar, and it can be visible from billions of light-years away. For that reason, mapping the distribution of quasars can help cosmologists understand the expansion rate of the Universe in an earlier era — and constrain the behavior of dark energy. My latest story in The Daily Beast explains:

If dark energy will be the same in billions of years as it seems to be today, the future will be dark and empty, as galaxies continue to move apart from each other at ever-faster rates. If dark energy comes and goes, though, maybe the rate of expansion will slow down again. All of this is a long time from now—trillions of years after the death of the Sun—but we might see hints about it today. We hope to see signs of what is to come by looking at how dark energy behaves now, and how it has acted in the past. Similarly, if dark energy is stronger in some parts of the cosmos, then certain pockets of the Universe would grow faster than in others. That also has implications for how the future cosmos looks. [Read more…]

Using Black Holes to Measure Dark Energy, Like a BOSS

Astronomers measured the rotation of a black hole from halfway across the Universe.

What, I need to say more?

Astronomers have now used gravitational magnification to measure the rotation rate of a supermassive black hole in a very distant galaxy. From four separate images of the same black hole, R.C. Reis, M.T. Reynolds, J.M. Miller, and D.J. Walton found it was spinning nearly as fast as possible. That likely means it was spun up by a small number of mergers with other black holes rather than a gradual increase from eating smaller amounts of mass.

This marks the first measurement of black hole rotation outside the local Universe…. [Read more]

Measuring black hole rotation halfway across the Universe

How did the biggest black holes form?

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. ]

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…]

Stephen Hawking, black holes, and scientific celebrity

The active galaxy Centaurus A, rendered in several different types of light. Note in radio waves (the central image at right), the galaxy itself seems to disappear, replaced by crossing jets of radio-emitting jets. Those are produced by the supermassive black hole at the galaxy’s core.

The active galaxy Centaurus A, rendered in several different types of light. Note in radio waves (the central image at right), the galaxy itself seems to disappear, replaced by crossing jets of radio-emitting jets. Those are produced by the supermassive black hole at the galaxy’s core.

For the upcoming ScienceOnline 2014 meeting, I’m leading a session titled “Reporting Incremental Science in a World that wants Big Results“. It’s an important topic. We who communicate science to the general public have to evaluate stories to see if they’re worth covering, then translate them in such a way that conveys their significance without hyping them (ideally at least). That’s challenging to do on deadline, and we’re not always or maybe even usually experts on the topics we report. I know a fair amount about cosmology and gravitational physics, but very little about galactic astronomy or planetary science — yet I must write about them, because it’s my job.

So Stephen Hawking’s recent talk on black holes is an interesting case study. I won’t rehash the whole story here, but I wrote not one but two articles on the subject yesterday. Article 1 was in Slate:

Hawking’s own thinking about black holes has changed over time. That’s no criticism: Evidence in science often requires us to reassess our thinking. In this case, Hawking originally argued that black holes violated quantum mechanics by destroying information, then backed off from that assertion based on ideas derived from string theory (namely, the holographic principle). Not everyone agrees with his change of heart, though: The more recent model he used doesn’t correspond directly to our reality, and it may not have an analog for the universe we inhabit. The new talk suggests he has now moved on from both earlier ideas. That’s partly what raises doubts in my mind about the “no event horizons” proposal in the online summary. Is this based on our cosmos or yet another imaginary one of the sort physicists are fond of inventing to guide their thinking? In my reading, it’s hard to tell, and in the absence of a full explanation we are free to project our own feelings about both Hawking and his science onto the few details available. [Read more…]

Article 2 was a follow-up on my own blog:

But at the same time, we have to admit that nobody—not Nature News, not Slate.com—would have covered a paper this preliminary had Hawking’s name not been attached. Other people are working on the same problem (and drawing different conclusions!), but they can’t command space on major science news sites. So, by covering Hawking’s talk, we are back on that treacherous path: we’re showing how science works in a way, but we risk saying that a finding is important because somebody famous is behind it. [Read more…]

Chandra space telescope image of an X-ray binary system containing a neutron star. [Credit: X-ray: NASA/CXC/Univ. of Wisconsin-Madison/S.Heinz et al; Optical: DSS; Radio: CSIRO/ATNF/ATCA]

Chandra space telescope image of an X-ray binary system containing a neutron star. [Credit: X-ray: NASA/CXC/Univ. of Wisconsin-Madison/S.Heinz et al; Optical: DSS; Radio: CSIRO/ATNF/ATCA]

About 380,000 years after the Big Bang, the Universe cooled off enough for stable atoms to form out of the primordial plasma. However, sometime in the billion years or so after that, something happened to heat the gas up again, returning it to plasma form. Though we know reionization (as it is called) happened, that epoch in the history of the cosmos is hard to study, so we don’t know exactly when and how the reheating happened. If a new proposed model is correct, though, ionization happened close to the end of that era, and was driven by binary systems containing a black hole or neutron star.

One new model, proposed by Anastasia Fialkov, Rennan Barkana, and Eli Visbal, suggests that energetic X-rays could have heated the primoridal gas to the point that reionization happened relatively rapidly. That’s in contrast with other hypotheses, which predict a more gradual reionization process. The X-rays in the new model were emitted by systems that include neutron stars or black holes. The nicest feature of the new proposal is that it predicts a unique pattern in light emission from the primordial gas, which could conceivably be measured by current radio telescopes. [Read more….]

Ionizing the Universe with black holes and neutron stars

The week in review (October 20-26)

Evidently, Nicole "the Noisy Astronomer" Gugliucci did not like it when I quoted Star Wars at her. All I said was "Aren't you a little short for a Stormtrooper?" [Credit: Melanie Mallon]

Evidently, Nicole “the Noisy Astronomer” Gugliucci did not like it when I quoted Star Wars at her. All I said was “Aren’t you a little short for a Stormtrooper?” [Credit: Melanie Mallon]

I had a wonderful time at GeekGirlCon; thanks again to Dr. Rubidium, AKA Nick Fury, for putting together the DIY Science Zone, and to everyone who made it a great event. I have a more formal wrap-up post in the works, but in the meantime, have some science writing.

  • The river of spacetime (Galileo’s Pendulum): As a follow-up to my earlier post, I extended the metaphor of dynamic spacetime. If spacetime is the river, gravity is the current, carrying matter and light along with it.
  • New type of quantum excitation behaves like a solitary particle (Ars Technica): In materials, the relevant entities aren’t particles, but quasiparticlesThese are quantum excitations that have mass, charge, spin, and all that jazz, but those properties depend on the specifics of the material…and of external influences. So, physicists would like to create quasiparticles that are less finicky, and behave more like free, solitary particles. That type of excitation is a leviton, and experimenters created them for the first time, as described in this new paper.
  • Taking Measure: A ‘New’ Most Distant Galaxy (Universe Today): It seems that every week, we see a new “most distant galaxy” announcement. However, this new find is special for two reasons: it’s a rare case where astronomers have measured the distance accurately using the galaxy’s spectrum, and the specific galaxy is producing new stars at a much higher rate than expected. Also, this is my first contribution to Universe Today!
  • For the love of Gauss, please stop (Galileo’s Pendulum): A somewhat ranting post in which I get grumpfy about the over-use and misuse of certain examples from the history of science in popular science writing.
  • What do we call a theory that is no longer viable? (Galileo’s Pendulum): As a follow-up to that previous post, I ponder better ways to think about the history of science, and propose (somewhat seriously) a term to describe theories that were once viable, but are now ruled out by evidence.