StarDate

Stars age in a well-understood way. Nuclear fusion in a star’s core converts lighter elements to heavier ones. At some point, that process ends and the star dies. How long the star lives and how it does so are determined by its mass.

But a recent study says that some stars could be powered in part by dark matter. That could affect how long the stars live, and make them look younger than they really are.

Dark matter accounts for about 85 percent of all the matter in the universe. It produces no energy. We know it’s there only because its gravity tugs the visible matter around it. It may consist of some type of subatomic particle, but no one’s found it.

But if certain types of dark-matter particles ram together, they may cancel each other with a flash. The study says that could impact stars in the center of the galaxy, where dark matter is tightly packed.

Massive stars, with stronger gravity, could pull in more dark matter. That would keep them going practically forever. And it would make them look younger. Lighter stars couldn’t pull in enough dark matter to keep them going. Instead, the dark-matter reactions would blow the stars apart.

A cluster at the heart of the galaxy contains many heavy stars that look young in some ways, but old in others. And the cluster doesn’t have any lightweight stars. That combination could mean that the evolution of the stars in that region is being influenced by dark matter.

Script by Damond Benningfield

Something small, dark, and heavy lurks at the heart of the Milky Way Galaxy. Most astronomers say it’s a black hole. But a recent study says “not so fast”- it could be a clump of dark matter.

The central object is called Sagittarius A-star. It’s about 4.3 million times the mass of the Sun. A few years ago, astronomers took a picture of its “shadow” against a glowing background.

Sagittarius A-star is encircled by stars and dusty clumps in tight orbits. They’re accelerated to millions of miles per hour by the gravity of the central object.

The new study suggested that object could be a knot of dark matter particles known as fermions. Dark matter produces no detectable energy, but its gravity pulls on the visible matter around it. It appears to make up about 85 percent of all the matter in the universe, but its nature remains unknown. The clump could account for many of the observed qualities of the central dark object.

Other studies have suggested that dark matter could produce fountains of gamma rays that shoot from the galaxy’s core. Dark-matter particles could produce the gamma rays when they ram together and cancel each other out.

The dark-matter model doesn’t explain all of the evidence of a black hole. But future instruments should be able to discern between the two models – providing a definitive explanation for the darkness at the galaxy’s heart.

More about dark matter tomorrow.

Script by Damond Benningfield

Our solar system is passing through one of the spiral arms that makes the Milky Way Galaxy look like a pinwheel. But the key words there are “passing through.” The solar system moves through the galaxy a little faster than the spiral arms do. So over hundreds of millions of years, we cross all of the galaxy’s major arms. And those crossings could be dangerous.

A spiral arm is a region where a passing wave squeezes giant clouds of gas and dust, triggering the birth of new stars. Many of the stars are especially hot and bright, so they light up the spiral arms.

The star-forming clouds are dense and turbulent. And a recent study suggested that could be where the “danger” comes in.

Researchers looked at tiny crystals in Earth’s crust. They found that the composition of the crystals varied over periods of hundreds of millions of years.

During some of those periods, Earth’s crust appeared to be especially hot. And the timing of those periods may correspond to passages through the spiral arms.

As we move through the dense clouds in the arms, big balls of ice and rock far from the Sun could be nudged inward. Some of them could ram into Earth, creating conditions that could account for some of the crystals. So while the Milky Way’s spiral arms may be beautiful, they may also be deadly.

Look for the glowing band of the Milky Way curving across the east as night falls, and arching high overhead later on.

Script by Damond Benningfield

The Milky Way shines at its best on summer nights. Right now, it arcs across the east as the sky gets fully dark, and passes high overhead later on. Under dark skies, it looks like a hazy band of light.

That band outlines the disk of our home galaxy. So for the astronomers who study the Milky Way Galaxy, it’s the go-zone – there’s lots to look at. But for those who study other galaxies, it’s been the no-go zone. In fact, it’s called the Zone of Avoidance, because it’s hard to see anything through it.

The main problem is giant clouds of dust scattered throughout the galaxy. The dust absorbs visible light. Depending on which part of the disk you look through, in fact, the clouds can block more than 99 percent of the light from objects behind them.

The other problem is that the Milky Way is crowded – millions upon millions of stars everywhere you look. So when you look into the band of the Milky Way, it’s hard to know whether you’re seeing a star or gas cloud in the galaxy or something beyond it.

Fortunately, some wavelengths that are invisible to the human eye do get through: infrared light and radio waves. The infrared is best seen from space, but the radio can be turned in by giant antennas on the ground. Galaxies typically emit more of both of those forms of energy than individual stars do – important ways to avoid problems from the Zone of Avoidance.

More about the Milky Way tomorrow.

Script by Damond Benningfield

It’s hard to map a forest when you’re standing in the middle of it. You see the trees that are close by, but most of the forest is blocked out. Astronomers have faced the same challenge when trying to map the Milky Way Galaxy. We’re right in the middle of it, surrounded by bright stars and dark dust clouds. So we can’t get an overall picture of the whole thing.

But nature has provided a way to see the forest through the trees: galactic radio. Big clouds of hydrogen gas emit radio waves at a wavelength of 21 centimeters – eight and a quarter inches. The radio waves pass through the intervening material, giving us a good outline of the structure of the Milky Way.

That wavelength is produced when hydrogen atoms get “bumped up” to a higher energy level. When the atoms drop back to their base level, they emit radio waves. This process plays out most commonly in clouds where new stars are being born.

Mapping the clouds revealed that the Milky Way is a spiral galaxy – a beautiful cosmic pinwheel. And measuring the motions of the clouds reveals how that pinwheel spins. So a lot of what we know about the Milky Way has come to us through the broadcasts of “galactic radio.”

The Milky Way arcs across the east as night falls. You need dark skies to see it. The center of the galaxy is in Sagittarius, which is low in the southeast. It’s easy to pick out because its stars form the outline of a teapot.

Script by Damond Benningfield