Dark Globs, a Salty Moon and More of This Week’s Stellar Wonders

Mysterious star clusters and Europa in a can feature in our picks for this week’s best space images

Weird dark clusters appear near a large galaxy, NASA creates a Jupiter moon in a can, Saturn's rings go razor-thin and more in our selection of the week's best space-related images.

Dark Globs

Something strange is afoot in the elliptical galaxy Centaurus A. In a recent survey of its star clusters, astronomers found that some are far more massive than they should be based on the matter we can see. The result suggests that a new and mysterious class of dark globular clusters may lurk around galaxies across the cosmos.

Globular clusters are loosely bound balls of old stars that orbit most galaxies. Astronomers can weigh them from afar and get a rough count of their stars based on brightness. Until now, such clusters usually had just the right amount of stars to account for their masses. But using ESO’s Very Large Telescope in Chile, astronomers have now found that most of the clusters in a sampling around Centaurus A have way more mass than their brightness suggests. These clusters may be packed with quiescent black holes, the scientists say, or they may contain large amounts of the mysterious substance known as dark matter. Either way, the finding challenges current theories of globular cluster formation.

Moon in a Can

Jupiter's moon Europa is a tantalizing place—an ice world thought to harbor a deep ocean that might be able to support life. Now, using a lab test that simulates the moon's composition, NASA researchers say the moon seems to be covered in dark streaks of sea salt. If so, Europa's surface may offer a rare glimpse at the contents of the moon's buried briny sea.

Europa's icy crust is lined with fissures that are covered with a mysterious dark substance. It's possible the coating comes from material erupting out of the moon's internal sea, but with limited data, it's hard to say for sure what the stuff is made of. However, scientists do know that Europa is bathed in radiation from nearby Jupiter, and that radiation should be chemically altering whatever is on the moon's surface. So NASA scientists created patches of simulated Europan ice sprinkled with potential culprits and bombarded them with radiation. They found that the patch containing regular table salt, aka sodium chloride, comes away looking very much like the real moon's surface fissures.

Dwarf Migration

For the first time, astronomers have caught a glimpse at older stars as they move from the crowded center of a galaxy cluster to its sparser outskirts. The result should help researchers figure out what happens to stars like our sun when they die.

In about 5 billion years, our sun will cool and expand to become a red giant. Over time it will lose much of its mass, until all that remains is a stellar core called a white dwarf. Current thinking is that most sun-like stars end their lives this way, with the bulk of their mass lost while the star is a red giant. Astronomers also have evidence that stars migrate to the outskirts of clusters as they lose mass. Now, a Hubble Space Telescope survey of white dwarfs in the star cluster 47 Tucanae shows this migration in action—and it reveals that relatively young white dwarfs are just starting out on their journey. This suggests that sun-like stars lose mass much later in their lifetimes than believed, altering our picture of how such stars burn out.

Northern Lights

At night in Scandinavia, light can create a panoply of displays. This image, snapped by an astronaut on board the International Space Station, shows Southern Scandinavia just before local midnight, with landmasses traced by the golden glow of artificial lights. In more rural zones, especially across Norway, moonlight reflects softly from the snow-covered ground. The shot also includes the brilliant green ribbon of an aurora seeming to run parallel with the bluish haze of distant sunlight filtering through Earth's atmosphere.

Crescent Saturn

The famous rings of Saturn are reduced to a small dark line just visible in the upper left of this image from NASA's Cassini spacecraft. The probe snapped the shot on May 13, and Flickr user Kevin Gill processed the raw data to create this serenely pastel view of the gas giant.

Saturn boasts eight main rings, making up a spectacular and dynamic system that spans about 175,000 miles outward from Saturn. All the rings are made of tiny particles of ice and rock, and when seen edge-on, the expansive adornments become razor-thin by comparison—some are only about 30 feet high, according to a recent "Ask Smithsonian" report.