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?”

Why are there three copies of each type of particle?

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The mystery of particle generations

Why are there three almost identical copies of each particle of matter?

For Symmetry Magazine:

The Standard Model of particles and interactions is remarkably successful for a theory everyone knows is missing big pieces. It accounts for the everyday stuff we know like protons, neutrons, electrons and photons, and even exotic stuff like Higgs bosons and top quarks. But it isn’t complete; it doesn’t explain phenomena such as dark matter and dark energy.

The Standard Model is successful because it is a useful guide to the particles of matter we see. One convenient pattern that has proven valuable is generations. Each particle of matter seems to come in three different versions, differentiated only by mass.

Scientists wonder whether that pattern has a deeper explanation or if it’s just convenient for now, to be superseded by a deeper truth. [Read the rest at Symmetry]

Pluto: what’s in a name?

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Pluto and Other Truly Epic Space Photos

For The Daily Beast:

To quote another great space adventurer: “Almost there!”

The New Horizons probe, launched in 2006, will finally reach Pluto next Tuesday, providing the first close-up view of the tiny, icy world since we discovered it in 1930. We’re already seeing features never glimpsed before. It’s a truly historic occasion, right up there with the Dawn mission to the giant asteroid Ceres, known since 1801 but never seen clearly before this year.

But what is Pluto? [Read the rest at The Daily Beast…]

Yes, I dive again into the “is or isn’t Pluto a planet”, and declare a pox upon both parties. Well, at least I call the IAU definition “crap” and make fun of the Pluto monomaniacs who insist that of course Pluto is a planet. Either way, though: I love Pluto, and I am very much looking forward to Tuesday.

P.S. Though we now have some excellent photos of Pluto and are getting more literally daily, the featured picture for my article is the bottom of a frying pan. Go figure.

We aren’t the dinosaurs: we’re the asteroid

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The Sixth Extinction: We’re Not The Dinosaurs, We’re The Asteroid

Yes, humans are probably to blame for the Earth’s sixth mass extinction event, which is wiping out species at a rate 53 times greater than normal.

For The Daily Beast:

Extinction is an inevitable consequence of evolution. Environments change, new species arrive and crowd out the old, any number of factors make a formerly successful species unsuccessful. No less an authority than Charles Darwin wrote in The Origin of Species, “Natural Selection almost inevitably causes much Extinction of the less improved forms of life and induces what I have called Divergence of Character.”

Even without the 19th-century capitalization for emphasis, extinction is a big deal. Earth has experienced at least five major mass extinction events, of which the end of the dinosaurs wasn’t even the largest. (The end of the dinos that hadn’t evolved into birds, of course.) Now the planet is experiencing the sixth mass extinction, and growing evidence points to the culprit. It’s not asteroids or volcanoes or methane this time.

It’s us. [Read the rest at The Daily Beast….]

A multitude of faint and fluffy galaxies

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Scientists Discover Hundreds of Hidden Galaxies

The new type of faint, fluffy galaxy might help resolve a cosmological conundrum

For The Daily Beast:

When we think of galaxies, we tend to focus on the beautiful spirals, like the Milky Way, or possibly the huge elliptical galaxies. However, we know that a lot of galaxies are small, and those are harder to spot. In fact, astronomers have observed far fewer low-mass galaxies than predicted by theory, which has been a puzzle and a problem.

A new discovery might help with the answer. Astronomers using the Subaru telescope in Hawaii found 854 nearly invisible galaxies in the Coma Cluster. These hidden objects are very large—some are roughly the size of the Milky Way—but extremely low density. This new census is a notable increase in the population of the Coma Cluster, which is already a large galaxy cluster. It’s likely that other galaxy clusters could be hiding fluffy faint galaxies too. [Read more in The Daily Beast…]

Emmy Noether and her wonderful theorem

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Mathematician to know: Emmy Noether

Noether’s theorem is a thread woven into the fabric of the science

For Symmetry Magazine:

We are able to understand the world because it is predictable. If we drop a rubber ball, it falls down rather than flying up. But more specifically: if we drop the same ball from the same height over and over again, we know it will hit the ground with the same speed every time (within vagaries of air currents). That repeatability is a huge part of what makes physics effective.

The repeatability of the ball experiment is an example of what physicists call “the law of conservation of energy.” An equivalent way to put it is to say the force of gravity doesn’t change in strength from moment to moment.

The connection between those ways of thinking is a simple example of a deep principle called Noether’s theorem: Wherever a symmetry of nature exists, there is a conservation law attached to it, and vice versa. The theorem is named for arguably the greatest 20th century mathematician: Emmy Noether.

So who was the mathematician behind Noether’s theorem? [Read the rest at Symmetry…]

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…]