The Care and Feeding of Black Holes

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

Part 2 of my 4-part series on black holes for Medium members is up; you can read part 1 here. If enough of you read, they may keep me around to write more, so please read and share!

The Care and Feeding of Black Holes

How intrinsically invisible objects become the brightest things in the universe

For Medium:

In the late 1950s, astronomers began spotting a number of bright sources of radio waves and visible light. These sources were pinpoints resembling blue stars, but further investigation showed they had to be something very different. For one thing, these quasi-stellar objects, as they were known then, were extraordinarily distant, much farther than any single star would be visible.

The spectra of these new quasi-stellar objects, or quasars, as physicist Hong-Yee Chiu abbreviated their name in 1964, showed they were emitting light through a completely different mechanism than starlight. The quantity of light quasars emitted to be visible across the universe meant they had to be driven by gravity.

Based on the data, astronomers concluded that each quasar was powered by a black hole millions or billions of times the mass of our sun. These supermassive black holes pull huge amounts of matter onto themselves, accelerating it until it glows very brightly. Additionally, the black hole jets a lot of matter away from itself rather than eating it, and those jets also glow intensely. These processes turn the ordinarily invisible black hole into something bright enough to see from billions of light-years away, outshining whole galaxies.

[read the read at Medium…]

Advertisements

No quantum foam seen in the cosmic beer glass

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

Light from distant black holes doesn’t surf on waves of quantum foam

Strongest check yet on quantum gravity effects in astronomy turns up nothing

For Ars Technica:

Quantum gravity is notoriously slippery. While the Standard Model successfully describes three forces of nature, it doesn’t include gravity, so gravity still has no consistent quantum theory. To make matters worse, gravity is so weak that it’s difficult to probe at the sorts of energies where any minuscule quantum effects would pop out. However, some researchers predict that those tiny effects could accumulate over cosmological distances: light traveling from far-off quasars would be changed by the “quantum foam” of spacetime, producing blurry images in our telescopes—or even making objects seem to disappear.

A new report by E. S. Perlman and colleagues examines the disappearance hypothesis using gamma-ray data from quasars. In particular, they investigated a possibility suggested by the holographic principle, the idea that all the information in the cosmos can be encoded on the two-dimensional boundary that encloses it. Disappointingly for fans of quantum foam, the gamma ray data did not show any measurable fading or blurring of the quasars.

As the authors point out, these results don’t rule out anything general regarding quantum gravity, quantum foam, or the holographic principle. But they do provide the tightest constraint yet on cumulative effects of quantum foam on light traveling across the Universe. [Read the rest at Ars Technica…]

We have a lot of reasons to be interested in the earliest stars that formed in our Universe. Particularly, these stars were the first to fuse hydrogen and helium into (nearly) all the heavier elements that exist today, including the carbon, oxygen, iron, calcium, and the like that make up life as we know it. However, not only are these stars too far away to observe directly, much their light is hidden by foreground sources, including our Milky Way. A new indirect observation may have solved that problem, though:

Now a study using the Fermi Gamma-ray Space Telescope has used the light emanating from supermassive black holes known as blazars to measure the diffuse light produced by reionization. When high energy gamma rays interacted with the ultraviolet photons produced by early stars, they were converted to particle/antiparticle pairs, and this creates a dropoff at a specific point in the blazar spectrum. This absorption was evident in a sample of 150 blazars, and the data can help constrain models of the very first stars in the Universe. [Read more…]

Early stars stole gamma rays from blazars