20 October 2015

How the Black Hole Saved General Relativity

Albert Einstein around the time he was
working on general relativity
It’s party time in the physics community. Scientists around the globe are starting to dust-off their tuxes and hem up their ball gowns.  Coming up in November is the hundredth anniversary of Albert Einstein’s most momentous achievement, his general theory of relativity that finally revealed to us how gravity works: collections of mass, like a star or planet, indent the very fabric of space-time, and we’re just sliding along the natural curved pathways. 

But all this centennial hoopla would have been a surprise to Einstein. It’s little remembered today, but right before Einstein’s death in 1955, general relativity was actually in the doldrums.  He even remarked to his collaborator Leopold Infeld that fellow physicists now “regard me as an old fool.” 

That’s because few universities were teaching general relativity, believing it had no practical applications.  The theory was more admired as an exquisite mathematical sculpture. After the flurry of excitement in 1919, when a famous solar eclipse measurement triumphantly provided the proof for Einstein’s new take on gravity (turning Einstein’s name into a synonym for genius), general relativity came to be largely ignored. Isaac Newton’s law of gravity worked just fine in our everyday world, so why be bothered? “Einstein’s predictions refer to such minute departures from the Newtonian theory,” noted one critic, “that I do not see what all the fuss is about.”  As a consequence, the best and the brightest moved into other realms of physics.  

But what his colleagues didn’t realize is that Einstein had devised a theory years ahead of its time.  Experimental measurements had to catch up to a model of gravity fashioned from pure intuitive thought.  Not until the final decades of the twentieth century when new astronomical tools revealed unexpected, highly energetic phenomena in the universe, did scientists take a second look at Einstein’s view of gravity. Newton’s laws fail when gravity is extremely strong, such as in quasars, neutron stars, and the celestial objects that did more to bring general relativity back to the forefront of physics than anything else—black holes.

The German astronomer Karl Schwarzschild started it all in 1915.  Just a few weeks after Einstein introduced his completed theory to the Prussian Academy of Sciences, Schwarzschild sent Einstein the first full solution, a way to map the gravitational field around a star. But, in doing so, Schwarzschild came upon an unexpected outcome: when the stellar mass was assumed to be a point in the center, a spherical region of space suddenly arose around that “singularity” out of which nothing—no signal, not a glimmer of light nor bit of matter—could escape.  If our Sun were compressed into a dot, this sphere (now known as the “event horizon”) would be about four miles wide.  Schwarzschild’s sphere wasn’t yet the bottomless pit of space-time known today but more an enigmatic boundary where matter vanished and time simply stopped. But no one worried.  Everyone, including Einstein, believed it wasn’t physically meaningful.  No star would ever collapse to a point, they grandly proclaimed, with other forces surely stepping in to save the day if such a fate were looming.

However, by 1930 Subrahmanyan Chandrasekhar at Cambridge University did prove that a star could collapse drastically, if weighty enough.  The young graduate student from India didn’t speculate on what happened to such a star, but nine years later at the University of California, Berkeley, J. Robert Oppenheimer and his student Hartland Snyder picked up the thread.  They saw that an aged stellar core, depleted of fuel and heavier than a certain mass, would enter into a state of permanent free fall, collapsing to a point and closing itself off from the rest of the universe.  They called it “continued gravitational contraction,” the first modern description of a black hole. 

Their finding swayed hardly anyone.  Astronomers still faced serious psychological hurdles in accepting such outrageous stellar behavior, as preposterous to them as continents moving around the Earth. Moreover, the Oppenheimer-Snyder paper was published the very day that Hitler marched into Poland, starting World War II. Collapsing stars seemed of little import at this tumultuous time; physicists had more urgent topics on their mind. 

It was not until the late 1950s that general relativity gradually revived after its decades-long lull.  A brief and misguided hope to discover “antigravity” led to private and military funding into general relativity, while the emergence of powerful computers allowed physicists to better simulate the death of stars. The epicenters for this relativistic Renaissance were in Moscow, under the guidance of the noted Soviet theorist Yakov Zel’dovich, and at Princeton University, where John Archibald Wheeler led forays into general relativity with a small army of students and post-docs.  

Illustration of black hole Cygnus X-1 stealing
gas from its companion star
Wheeler actually started out to prove that Oppenheimer’s stellar Armageddon could not possibly happen.  Getting rid of the singularity was his goal. But in the end he only convinced himself and others that the black hole was inevitable. Observations eventually backed him up. Starting in the 1960s, spaceborne sensors soon spotted powerful X rays and gamma rays streaming from points around the celestial sky, identifying where black holes release huge energies as matter plunges toward them, before disappearing behind the dark curtains of their event horizons.  It took around half a century for physicists to at last cry uncle and admit that Schwarzschild’s singularity was real.

Where once the field of general relativity was a cozy backwater, it now flourishes, thanks to the black hole.  No longer oddities, black holes are a vital component of the universe. One is formed somewhere in the universe with each tick of the clock. More than that, every fully developed galaxy appears to have a supermassive black hole at its center; it may be that the very existence of a galaxy—and, in turn, us—depends on it. 

John Wheeler once remarked that he never read science fiction. “All the science fiction I need,” he aptly noted, “is right out there in front of us.”  

15 October 2015

Now There's a Drop to Drink

Percival Lowell in 1914 at the eyepiece of his
24-inch telescope at the Lowell Observatory in Arizona

NASA just released its latest news concerning water on Mars; liquid water appears to be creating streaks on Martian slopes.  

For more on the person who started this whole conversation about water on Mars more than a century ago, click here to see my latest column for Natural History magazine.  

10 August 2015

Rings, Rings, Rings

In my latest Natural History column, I write about the solar system's Lord of the Rings―Saturn.  Galileo led the way. Click here to check it out.

21 November 2014

Wild Rays

Cosmic rays are mostly protons, but can also be atomic nuclei or electrons.  So, why are they called cosmic "rays?"  To find out, click here to check out my latest story in Natural History magazine.

Part of the Telescope Array, a cosmic-ray detector in western Utah (Ben Stokes, University of Utah)

03 May 2014

Who Originated the Name "Black Hole?"

In my latest column in Natural History magazine, I discuss the origin of the term "black hole." For many decades, the Princeton physicist John Archibald Wheeler was credited with coining the term.  But he likely borrowed it from someone else.  Click here to check out the story.

26 June 2013

Mapping Our Cosmic Main Street

Milky Way seen from Kitt Peak National Observatory
Despite the fact that we can peer outward with our telescopes into deep space for billions of light-years, our local celestial landscape is downright murky.  I write about this conundrum in my latest Natural History column, where I discuss how astronomers first tried to map the Milky Way's spiraling arms. Click here to check it out.

09 February 2013

The Solar System Police

Once a planet
Pluto was not the first planet to be demoted. Another solar system object was not only demoted from planetary status but got re-promoted later. Read about in my latest column in Natural History magazine. Click here.

Image Credit: Hubble Space Telescope

25 September 2012

Cosmic Cradles

In 1995 Robert Williams had a crazy idea.  Then director of the Space Telescope Science Institute, he decided to use his allocated time on the Hubble Space Telescope to train its mirror on one tiny spot of the skya dark, starless region near the handle of the Big Dipper.  Over ten consecutive days the telescope took a series of 342 time-exposure photographs, images that were combined and computer-enhanced to produce the most deeply penetrating astronomical picture of its time.  It was called the Hubble Deep Field.  

What this stunning picture revealed were some 2,000 galaxies in different stages of development.  Like a geological core sample, it displayed galaxies in the local, intermediate, and distant universe altogether, out to some 12 billion light-years. 

Now a team of astronomers has assembled the eXtreme Deep Field, or XDF for short.  They've combined ten years worth of data taken by Hubble (some 2,000 images in all) from a patch of sky in the constellation Fornax.  This one digs some 13.2 billion years back into time, to just half a billion years after the Big Bang. 

Hubble's eXtreme Deep Field
All I can say upon gazing at this image is, "Wow!"  How can anyone doubt the possibility of other life beyond the solar system when we have these myriad cosmic cradles sprinkled through space and time.

18 June 2012

Remarkable Odyssey

Jane Luu

My congratulations go out to Jane Luu (MIT Lincoln Laboratory), David Jewitt (UCLA), and Michael Brown (Caltech) for winning this year's prestigious Kavli Prize in astrophysics, which includes a cash award of $1 million.  In 1992 both Luu, then at Harvard, and Jewitt, who was based at the University of Hawaii at the time, discovered the first large object orbiting the Sun beyond Neptune and Pluto. They quickly found others as well.  Brown followed up in 2005 by finding Eris, an object about the same size as Pluto but with nearly a third more mass.  

All in all, these three astronomers proved the existence of the "Kuiper belt," a disk of icy planetesimals long proposed to lie beyond the outer planets of our solar system.  Their discoveries ultimately caused Pluto to be demoted to "dwarf planet," joining its more similar companions in the belt.  

I was particularly thrilled for Jane, who I profiled in 1996 for Astronomy magazine.  Click here to read how Jane's life journey took her from war-ravaged Vietnam to the outer reaches of our solar system.

Image Credit: MIT Lincoln Laboratory

15 May 2012

Chasing Galaxies

Beatrice Tinsley
In this era that offers us such wondrous pictures of galaxies, showing their vivid evolution over the eons, it's easy to forget that astronomers once thought galaxies evolved relatively little after their initial formation in the early universe.  And the woman primarily responsible for changing that view was Beatrice Tinsley. She is said to have "changed the course of cosmological studies." Click here to read about this story in my latest column in the April issue of Natural History. 

03 April 2012

Curiouser and Curiouser

The bright star Sirius
and its tiny white-dwarf
companion. (Credit: The
McDonald Observatory)
One hundred and fifty years ago, two astronomers in Cambridgeport, Massachusetts, were testing the lenses of a new telescope they were building and in the process discovered an entirely new cosmic creature (although it took a while to figure that out).  Click here to read more about it in my latest column for Natural History magazine. Happy Anniversary, white dwarf star!

26 January 2012

An Unfettered Mind

I have another book review out, published in the Washington Post on Sunday, January 22.  This time the book is Stephen Hawking: An Unfettered Mind, by science writer Kitty Ferguson.  It's a new edition of an earlier biography of Hawking that Ferguson published in 1991.

30 November 2011


Check out my latest book review, published in the Washington Post on November 13.  The book is titled Radioactive. It's an intriguing, visual work about Madame Curie and her husband Pierre.  The author is Lauren Redniss, who is both a writer and artist. Each skill is on beautiful display in this unusual presentation. Below, a sample of two of its 210 pages. 

28 September 2011

Fried Egg Nebula

Does the universe want bacon with that?

Fried Egg Nebula
An international team of astronomers recently used the European Southern Observatory's Very Large Telescope in Chile to capture a unique picture of a hypergiant star situated about 13,000 light-years from Earth in the direction of the constellation Scorpius.  For obvious reasons, they've playfully named it the Fried Egg Nebula.  

This humongous yellow star shines half a million times more brightly than our Sun (is there a sunblock strong enough?) and is a thousand times bigger. If it replaced our Sun, this 20-solar-mass star would almost engulf Jupiter.  Earth would be toast.

This star is quite active, hence the two spherical shells of dust and gas that surround the central star, setting up the fried-egg appearance.  This material was jettisoned outward in a series of explosive bursts over the last few hundred years.  When this hypergiant finally dies as a brilliant supernova some day, watch out! 

Image Credit: ESO/E. Lagadec

15 August 2011

Who Gave the Black Hole Its Name?

John Wheeler in Black Hole, Nova Scotia, 1981
Book after book attributes the phrase "black hole" to the Princeton physicist John Archibald Wheeler, who in the 1960s re-energized the field of general relativity by helping prove that if certain dying stars were massive enough they would not settle down as neutron stars but continue to collapse to a point, digging a pit into space-time. 

Wheeler liked to tell the tale that he first used the term at a 1967 conference, quickly set up at the NASA Goddard Institute for Space Studies in New York City once pulsars were discovered. Were the pulsars' mysterious beeps coming from red giant stars, white dwarfs, neutron stars?  Wheeler told the assembled astronomers they might be the "gravitationally collapsed objects" that he studied.  “Well, after I used that phrase four or five times, somebody in the audience said, ‘Why don’t you call it a black hole.’ So I adopted that,” Wheeler told me.   He used the phrase again several weeks later during an after-dinner talk at the annual meeting of the American Association for the Advancement of Science (AAAS) in New York City on December 29, 1967.  It made it into print when an article based on that talk, titled “Our Universe: The Known and the Unknown,” was published in American Scientist in 1968. 

But it turns out the term was already in the air.  It had been circulating among conferees four years earlier at a symposium on relativistic astrophysics held in Texas at the end of 1963. The proof?  Life magazine science editor Albert Rosenfeld mentioned black holes in his report on the conference. And the term was used again a few weeks later at the 1964 American Association for the Advancement of Science meeting held in Cleveland.  Ann Ewing of Science News Letter reported that astronomers and physicists at the conference were suggesting that “space may be peppered with ‘black holes.’” 

But it's certainly true that the phrase didn’t catch fire until 1967.  It seemed to need the imprimatur of John Wheeler, the dean of American general relativity, to give it gravitas.  Once Wheeler gave his blessing, the phrase began popping up in the official scientific literature—although over the first year it was usually denoted as “the black hole,” an expression so exotic it needed to be constrained within quotation marks. 

06 July 2011

Only Your Astrophysicist Knows for Sure

Is the universe planning to turn blonde?

The Rho Ophiuchi star formation region
Using a telescope perched high in the Chilean Andes, an international team of astronomers discovered molecules of hydrogen peroxide, the chemical that bleaches hair, in a dense cloud of gas and dust near the star Rho Ophiuchi some 400 light-years distant.  

This find is more than an amusing curiosity. Hydrogen peroxide is formed when two hydrogen atoms link up with two oxygen atoms (H2O2), a pair of elements critical for life. Moreover, take just one oxygen out of hydrogen peroxide and you get water (H2O). So, further study of this molecule's chemistry out in deep space may help astronomers better understand the formation of water in the universe.  
Image Credit: ESO/S. Guisard 

29 June 2011

The Ever-Changing Record

I smiled when I heard the news.  An international team of astronomers has just announced the discovery of the most distant quasar, the luminous core of a young and active galaxy situated a whopping 12.9 billion light-years away.  That means the light from this quasar, likely generated as matter falls into a supermassive black hole, started on its journey just 770 million years after the Big Bang. 

This image of the record-setting quasar, ULAS J1120+0641, was
created from images taken from surveys made by both the Sloan
 Digital Sky Survey and the United Kingdom Infrared Telescope Deep
Sky Survey. The quasar appears as a faint red dot close to the center.

I smiled because this headline has been regularly appearing in the news for nearly half a century, ever since Caltech astronomer Maarten Schmidt recognized the first quasar in 1963.  Known as 3C 273, from its listing in a catalog of radio sources, Schmidt's quasar was about 2 billion light-years distant: small potatoes now but a huge cosmic distance in its day.  

Over the years, the most-distant-quasar record has gotten replaced as often as a newborn's diapers.  But now the distances are so great that they present some problems: the light from this newfound quasar suggests that the quasar is being powered by a black hole about two billion times more massive than our Sun. How did such a gargantuan object grow so quickly in the early days of the universe? As team member Daniel Mortlock, of Imperial College London, notes, "It's like rolling a snowball down the hill, and suddenly you find that it's 20 feet across!" Theorists will surely be putting on their thinking caps to find a way.

15 June 2011

Chicken or the Egg Question Answered?

One of the most fascinating findings in astronomy over the last decade has been the unique relationship between galaxies and the supermassive black holes lurking in their centers.  Rather than being rare, a giant black hole appears to reside in each and every elliptical or spiral galaxy throughout the cosmos.

Illustration of an active, supermassive
black hole in a galaxy's center
But which came first? The giant black hole, drawing in material to help form the galaxy, or did the galaxy form first, generating the environment for a dense collection of matter to collapse into a black hole at its heart?  

Astronomers and theorists from Yale, Rutgers, and the Universities of Hawaii and Michigan have now gathered evidence suggesting that each galaxy and its black hole grow in tandem, starting less than a billion years after the Big Bang.  As reported in the journal Nature, the team revealed this by looking at some 250 distant galaxies earlier spotted by the Hubble Space Telescope and searching with the Chandra X-Ray Observatory for the x-ray signals being emitted from each galaxy's central black hole.  What they find is a distinct connection: the black holes growing and evolving over time along with their host galaxies. "This finding," says team member Kevin Schawinski of Yale University, "tells us there is a symbiotic relationship between black holes and their galaxies that has existed since the dawn of time."  
Image Credit: NASA Goddard Space Flight Center

05 April 2011

In a Grain of Sand

There is something new under the Sun.  And it took some 42 years to find it.

In 1969, members of the Japanese Antarctic Research Expedition found nine meteorites lying on an icy field in the continent's Yamato Mountains.  Ever since, these specimens (along with the 40,000 meteorites collected in Antarctica afterward) have been avidly studied. Yet, even after four decades of analysis, some surprises remained. 

U.S. field team in Antarctica searching for meteorites in 1988-89.

One of the 1969 meteorites, known as Yamato 691, was recently examined with a transmission electron microscope located at NASA's Johnson Space Center in Houston, Texas.  This 21st-century nanotechnology allowed researchers from the United States, South Korea, and Japan to zoom in on isolated grains in the meteorite that are less than a hundredth the width of a human hair.  And what they discovered was an entirely new type of mineral, different from the 4,500 minerals already recognized by the International Mineralogical Association.  The researchers dubbed it "Wassonite," in honor of UCLA professor John Wasson, an international meteorite expert. 

Wassonite is made out of only two elements, sulfur and titanium.  Yet these atoms join up to form a crystalline structure that has not been previously observed in nature.  The mineral formed some 4.5 billion years ago, likely as part of an asteroid orbiting between Mars and Jupiter.  Further study of the novel crystal promises to offer new insights on conditions in the early solar system. "In the words of the great English poet William Blake," says Simon Clemett, a space scientist at the Johnson Space Center and co-discoverer of the new mineral, "we are now able 'to see the world in a grain of sand.'"
Picture Credit: Department of Earth and Planetary Sciences, Washington University in St. Louis

09 March 2011


A common refrain from my science-writing students is, "Where do you get story ideas?"

A good place to start is hanging out with graduate students and post-docs, who are often thinking and working on problems at the cutting edge.  Many of my best magazine articles when I was starting out involved the work of these pioneering newcomers (many of whom are now the leading lights in their fields). 

If those interested in writing on astronomy can't make a personal university visit to find out what's on a graduate student's mind these days, there's a new website that offers the next best thing: Called "astrobites," it's a daily astrophysical literature journal written by graduate students for undergraduates.  It beautifully fulfills its named mission―providing up-to-date summaries of the latest research in easy-to-go-down write-ups.  The graduate students who post these reports―from Harvard, Michigan, UC Santa Cruz, Colorado, Arizona―aim to make active research areas enticing and accessible to undergraduates, but it serves just as well as a convenient overview for journalists seeking hot new topics popping up in the field of astronomy and astrophysics. 

Christmas Tree Nebula: Here just because it's pretty.