FromDennis Overbye at The New York Times: Birth of a Star

New York Times

The New York Times

In galactic nurseries like the Orion Nebula, clouds of gas and dust mingle, birthing new stars and planetary systems. The ALMA radio telescope made a recent observation of possible planets being born.

In one of the most detailed astronomical images ever produced, NASA/ESA’s Hubble Space Telescope captured an unprecedented look at the Orion Nebula. … This extensive study took 105 Hubble orbits to complete. All imaging instruments aboard the telescope were used simultaneously to study Orion. The Advanced Camera mosaic covers approximately the apparent angular size of the full moon.

NASA Hubble Telescope
NASA Hubble schematic

Hubble’s Advanced Camera for Surveys

We might be stardust, Joni Mitchell sang of Woodstock in 1969, echoing what was already a half-century of hard-headed astronomical truth. But astronomers have struggled to understand just exactly how stardust goes from being cosmic smog, littering the lanes of the galaxy, to planets and people.

Recently, however, astronomers using the Atacama Large Millimeter/submillimeter Array, or ALMA, an international radio telescope in the high desert of Chile, obtained what might be the best picture yet of dust in the act of turning into planets.

ALMA Array
ALMA Array

It shows a young star named HL Tauri, about 450 light-years from here and thus in the constellation of Taurus. The star is surrounded by a glowing disk of dust and gas about 22 billion miles across — about four times the size of Neptune’s orbit, which bounds the realm of official planets in our own solar system ever since the outlier Pluto was bounced from the fraternity of planets.

HL Tauri

Produced by: Jason Drakeford, Jonathan Corum and Dennis Overbye

Most significant, the disk is scored with dark rings or grooves, like a record or the rings of Saturn.

That, the ALMA astronomers who took the picture say, is most likely the signature of a new planetary system in the making. As clumps of dust accumulate and grow into planets at various distances from the star, they gobble up the dust near them, scouring clear paths around the star and leaving a pattern of bright and dark rings, explained Catherine Vlahakis, an ALMA astronomer.

The ALMA picture represents only the end of the beginning of a long cycle of birth and death for stars and planets.

It begins in galactic nurseries like the Orion nebula, where Christmas-colored clouds of gas and dust mingle primordial elements left over from the Big Bang with the ashes of more recent stars that have died and exploded. Rumbled by explosions and raked by radiation and winds from new stars, the clouds collapse under their own weight.

The result is a cosmic baby boom. Space in Orion is littered with small globs of gas and dust, harboring baby stars and their planets in the making. Stellar tadpoles, if you like, in a cloudy pond.

It can take a million years or so for clouds as massive as the Sun to collapse to the dimensions of a solar system. As they shrink, their centers spin up into swirling maelstroms, protostars surrounded by protoplanetary dust.

If the cloud is big enough, gravity will eventually compress it to the point that it is hot enough to ignite thermonuclear reactions — a star is born and begins to burn its way out of its birth bag.

At the same time, radiation from powerful stars nearby is eating away the cocoon from the outside, setting up a deadly race. Too much radiation from the outside will burn off not only the cocoon but the disk around the new star as well, leaving it naked and alone, without the potential for planets. Luckily that didn’t happen here.

If the disk survives, irregularities in it can grow — first by electrical forces as particles randomly collide and stick, then by gravity as clumps attract one another and sweep their orbits clean like the dark grooves of HL Tauri.

Astronomers estimate that HL Tauri is only a million years old, a blink in the long lifetime of a star. In an email Dr. Vlahakis said that stars this young had not been expected to have planets big enough to gouge grooves in their planetary disks so soon. “This suggests that planet formation might happen faster than previously thought,” she said.

Astronomers have recently estimated that there are at least as many planets in the Milky Way as there are stars. What is happening here has happened billions of times already in the galaxy. The putative planets of HL Tauri have millions or billions of years to make something more of themselves. Life got lucky once in the Milky Way — what are the odds it could happen again?

See the full article here.

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