Star

Watch How Stars Will Move Over the Next 5,000,000 Years

The European Space Agency (ESA) recently published a video featuring data from their Gaia mission. Gaia is an effort to make a 3D map of the Milky Way. This entails figuring out where all the billion stars in our galaxy are, how they’re moving, and how fast. It’s a big job.

In the video, we see data for 2,081,370 stars moving over a simulated period of 5,000,000 years starting in roughly 2014. Each frame in the video simulates 750 years of movement. As…

Einstein’s latest anniversary marks the birth of modern cosmology

Andromeda galaxy
Edwin Hubble’s observations of stars in the Andromeda galaxy (shown) demonstrated that the universe was vastly bigger than Albert Einstein realized. Nevertheless, Einstein’s paper applying his general theory of relativity, published a century ago, became the foundation for the modern science of cosmology.

First of two parts

Sometimes it seems like every year offers an occasion to celebrate some sort of Einstein anniversary.

In 2015, everybody lauded the 100th anniversary of his general theory of relativity. Last year, scientists celebrated the centennial of his prediction of gravitational waves — by reporting the discovery of gravitational waves. And this year marks the centennial of Einstein’s paper establishing the birth of modern cosmology.

Before Einstein, cosmology was not very modern at all. Most scientists shunned it. It was regarded as a matter for philosophers or possibly theologians. You could do cosmology without even knowing any math.

But Einstein showed how the math of general relativity could be applied to the task of describing the cosmos. His theory offered a way to study cosmology precisely, with a firm physical and mathematical basis. Einstein provided the recipe for transforming cosmology from speculation to a field of scientific study.

“There is little doubt that Einstein’s 1917 paper … set the foundations of modern theoretical cosmology,” Irish physicist Cormac O’Raifeartaigh and colleagues write in a new analysis of that paper.

Einstein had pondered the implications of his new theory for cosmology even before he had finished it. General relativity was, after all, a theory of space and time — all of it. Einstein’s showed that gravity — the driving force sculpting the cosmic architecture — was simply the distortion of spacetime geometry generated by the presence of mass and energy. (He constructed an equation to show how spacetime geometry, on the left side of the equation, was determined by the density of mass-energy, the right side.) Since spacetime and mass-energy account for basically everything, the entire cosmos ought to behave as general relativity’s equation required.

Newton’s law of gravity had posed problems in that regard. If every mass attracted every other mass, as Newton had proclaimed, then all the matter in the universe ought to have just collapsed itself into one big blob. Newton suggested that the universe was infinite, filled with matter, so that attraction inward was balanced by the attraction of matter farther out. Nobody really bought that explanation, though. For one thing, it required a really precise arrangement: One star out of place, and the balance of attractions disappears and the universe collapses. It also required an infinity of stars, making it impossible to explain why it’s dark at night. (There would be a star out there along every line of sight at all times.)

Einstein hoped his theory of gravity would resolve the cosmic paradoxes of Newtonian gravity. So in early 1917, less than a year after his complete paper on the general theory was published, he delivered a short paper to the Prussian Academy of Sciences outlining the implications of his theory for cosmology.

In that…

Magnetism helps black holes blow off gas

GRO J1655-40
WIND POWER A black hole steals gas from a normal star in this artist’s illustration of the binary star system GRO J1655-40. Most of the gas is pulled into an inward-spiraling disk (red) around the black hole, but winds driven by magnetic fields blow some gas away.

Black holes are a bit like babies when they eat: Some food goes in, and some gets flung back out into space. Astronomers now say they understand how these meals become so messy — and it’s a trait all black holes share, no matter their size.

Magnetic fields drive the turbulent winds that blow gas away from black holes, says Keigo Fukumura, an astrophysicist at James Madison University in Harrisonburg, Va. Using X-rays emitted from a relatively small black hole siphoning gas from a nearby star, Fukumura and colleagues traced the winds flowing from the disk of stellar debris swirling around the black hole. Modeling these winds showed that magnetism, not other means, got the gas moving in just the right way.

The model was previously used to explain the way winds flow around black holes millions of times the mass of the sun. Showing that the model now also works for a smaller stellar-mass black hole suggests that magnetism may drive winds in black holes of all sizes. These results, published online March 6 in Nature Astronomy, could give clues to how black holes consume and expel matter and also to why some galaxies stop forming stars.

Astronomers first proposed that magnetic fields powered the winds around black holes in the 1970s, but the idea has been controversial. Directly observing the winds is impossible. Their existence is inferred by a black hole’s X-ray spectrum — an inventory of light…