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]

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Some heavy facts about gravity

[ This blog is dedicated to tracking my most recent publications. Subscribe to the feed to keep up with all the science stories I write! ]

I’m not generally the type of writer who makes listicles, but I’m producing a few for Symmetry Magazine this year. The first covers the OG of fundamental forces: gravity!

Six weighty facts about gravity

Perplexed by gravity? Don’t let it get you down

For Symmetry Magazine:

Gravity: we barely ever think about it, at least until we slip on ice or stumble on the stairs. To many ancient thinkers, gravity wasn’t even a force—it was just the natural tendency of objects to sink toward the center of Earth, while planets were subject to other, unrelated laws.

Of course, we now know that gravity does far more than make things fall down. It governs the motion of planets around the Sun, holds galaxies together and determines the structure of the universe itself. We also recognize that gravity is one of the four fundamental forces of nature, along with electromagnetism, the weak force and the strong force.

The modern theory of gravity—Einstein’s general theory of relativity—is one of the most successful theories we have. At the same time, we still don’t know everything about gravity, including the exact way it fits in with the other fundamental forces. But here are six weighty facts we do know about gravity. [Read the rest at Symmetry Magazine]

Be very very quiet, we’re hunting gravitational waves

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Gravitational waves and where to find them

Advanced LIGO has just begun its search for gravitational waves

For Symmetry Magazine:

For thousands of years, astronomy was the province of visible light, that narrow band of colors the human eye can see.

In the 20th century, astronomers pushed into other kinds of light, from radio waves to infrared light to gamma rays. Researchers built neutrino detectors and cosmic ray observatories to study the universe using particles instead. Most recently, another branch of lightless astronomy has been making strides: gravitational wave astronomy.

It’s easy to make gravitational waves: Just flap your arms. Earth’s orbit produces more powerful gravitational waves, but even these are too small to have a measurable effect. This is a good thing: Gravitational waves carry energy, and losing too much energy would cause Earth to spiral into the sun. [Read the rest at Symmetry Magazine…]

 

I Love Q, and now you can too!

I wrote a feature story for Physics World on an interesting little discovery about neutron stars, but unfortunately the article wasn’t in their free online edition. HOWEVER, the editors have kindly let me repost the article here in PDF format for free download! (Here’s the summary I wrote a few weeks ago.)

Physics World is a glossy magazine published by the Institute of Physics (IoP) in Europe. My articles are in the print version, but you can access them online by joining IoP (US$25 per year) and see everything they publish either through the Physics World website (which also has tons of free content) or the app, available on iTunes or Google Play.

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?”

The three little words every pulsar wants to hear

[ This blog is dedicated to tracking my most recent publications. Subscribe to the feed to keep up with all the science stories I write! UPDATE: you can now download this article in PDF format! See the follow-up post or the update below.]

I can’t help falling in Love with Q

The first page of my latest print article in Physics World. Unfortunately, there doesn't seem to be an online version.

The first page of my latest print article in Physics World. Unfortunately, there doesn’t seem to be an online version.

From Physics World:

The dancers are an elegant pair. Clothed in the fabric of space–time, they are driven by the music of gravity and make a stately orbit around one another once every two-and-a-half hours. They pirouette as they move – one spins once every few seconds while the other spins many times per second – and each one of their twirls is marked by an intense flash of light. The dancing partners are pulsars – spinning neutron stars that send a regular blip of light our way.

Named PSR J0737-3039, this duo is one of a kind. More commonly known as the “double-pulsar system”, it is the only two-pulsar system where we have observed both partners. Other binary-pulsar systems exist, consisting of a pulsar and, for example, a white dwarf or a (non-radiative) neutron star. However, astronomers find the double-pulsar system particularly valuable because it consists of two flashing beacons rather than one, and the more information they can glean to test their theories, the better.

Unfortunately, this article is currently only available in print, and Physics World isn’t a typical newsstand offering. Update: the editors have kindly let me repost the article here in PDF format for free download! You can also access all the content online by joining IoP (US$25 per year) and see everything they publish either through the Physics World website (which also has tons of free content) or the app, available on iTunes or Google Play.

I am overly proud of the headline, and the concepts I described in the article are very interesting. In brief, measurable properties of neutron star exteriors are independent of the particular physics going on inside. Since neutron stars are some of the most complex objects we know of — they are the density of an atomic nucleus, the mass of a star, and the size of a city on Earth — anything we can learn to help study them is a good thing. A few theorists figured out how to relate observable properties to each other, in particular three parameters labeled I, Q, and the “Love number” (named for a person, not the emotion). The I-Love-Q relations in combination with sophisticated neutron star observations could hopefully help us solve the deep mystery of what’s going inside an object that’s like nothing we can create in the lab.

(If you want some more technical information, here’s the main paper I drew on for background.)

Why do some want to modify general relativity?

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And yes, I did refer to MOND as “a fungus in the basement of astronomy”.

Do We Need to Rewrite General Relativity?

For NOVA “The Nature of Reality”:

General relativity, the theory of gravity Albert Einstein published 100 years ago, is one of the most successful theories we have. It has passed every experimental test; every observation from astronomy is consistent with its predictions. Physicists and astronomers have used the theory to understand the behavior of binary pulsars, predict the black holes we now know pepper every galaxy, and obtain deep insights into the structure of the entire universe.

Yet most researchers think general relativity is wrong.

To be more precise: most believe it is incomplete. After all, the other forces of nature are governed by quantum physics; gravity alone has stubbornly resisted a quantum description. Meanwhile, a small but vocal group of researchers thinks that phenomena such as dark matter are actually failures of general relativity, requiring us to look at alternative ideas. [Read the rest at NOVA…]