StarDate

The Moon anchors a prominent triangle in tomorrow’s early-morning sky. The pattern is well up in the east at first light. The stars Pollux and Castor – the twins of Gemini – line up to the upper left of the Moon, with Mars to the upper right. The brilliant planet Jupiter stands well below the triangle.

Mars and Pollux are almost exactly the same brightness right now. And they’re the same color: orange. But they achieve that color in different ways.

Mars is a planet – a ball of rock and metal that’s smaller than Earth. Its color comes from iron oxide – particles of rust – in the rocks and dust that cover most of its surface. The rust probably formed when iron-rich rocks interacted with liquid water on the surface. But there’s no water on the surface today. So the rocks must have rusted billions of years ago, when Mars was much warmer and wetter than it is today. As the rocks eroded, the Martian winds carried the dust around the globe – enhancing the color of the Red Planet.

Pollux, on the other hand, is a star. It completed the prime phase of life, then puffed up to giant proportions – about nine times wider than the Sun. As it expanded, it got cooler. And a star’s color is determined by its surface temperature; cool stars look red or orange. So just by looking at it, we can tell that Pollux is thousands of degrees cooler than the Sun.

We’ll talk about the Moon and Jupiter tomorrow.

Script by Damond Benningfield

Some of the most imposing features on Mars are its giant volcanoes. The largest is Olympus Mons. It’s more than 13 miles high, and covers an area as big as New Mexico. It’s part of the largest complex of volcanoes on the planet – a region called Tharsis Ridge.

The second-largest group is on Elysium Rise. Its largest member is Elysium Mons. It’s the fourth-highest mountain on the planet. It has an elevation of about 10 miles above the Martian equivalent of “sea level,” and it towers about eight miles above the surrounding plains.

Like the other major volcanoes, it’s extinct – or at least dormant. It probably hasn’t erupted in hundreds of millions of years. It formed over billions of years, from layers of lava and ash. It’s marred by many craters.

Some of them are impact craters, carved by giant space rocks. Others may be volcanic vents, formed by side eruptions of gas or lava.

The volcanoes on Mars have grown so big mainly because there are no plate tectonics. Once a pool of magma forces its way to the surface, it just keeps going – the crust above it doesn’t move away. So there’s no “cut-off” valve – the volcano erupts as long as there’s molten rock below to keep feeding it – building some giant mountains on the Red Planet.

Mars appears below the Moon in tomorrow’s early morning sky. It looks like a fairly bright orange star.

More about the Moon and its companions tomorrow.

Script by Damond Benningfield

Little Red Dots might be like Tootsie Roll Pops: colorful on the outside, dark on the inside. They may consist of a glowing cloud of gas and dust encircling a supermassive black hole. And they could be telling us about the birth of the first big black holes in the universe.

Little Red Dots were first seen in 2022, by Webb Space Telescope. Since then, it’s discovered hundreds of them. They’re compact but extremely bright. And they’re so far away that we see them when the universe was no more than about one-tenth of its current age.

Astronomers have proposed several explanations for them. One is the idea of a black hole surrounded by gas and dust.

A recent study looked at a dot that was behind a huge cluster of galaxies. The cluster’s gravity magnified the view of the dot, making it easier to suss out its details. Its heart is a black hole about 50 million times the mass of the Sun. The surrounding cloud is no more than half that mass. As material in the cloud funnels inward, it gets hot, lighting up the rest of the cloud. The gas and dust absorb blue light, so we see only red.

Astronomers have pondered the formation of early galaxies for decades. They’ve wondered whether the giant black holes in their hearts formed first, or if the galaxy came first and the black hole formed later.

The new finding suggests that, in at least some cases, the black hole came first – born at the heart of a Little Red Dot.

Script by Damond Benningfield

In the past decade, astronomers have “heard” almost 400 mergers between black holes. The signals were carried by gravitational waves – tiny ripples in spacetime. They’ve revealed that some of the black holes probably had undergone earlier mergers – making them third-generation black holes.

Gravitational waves are produced by the motions of any object. But the waves are extremely weak. So far, the only ones that have been detected were produced by mergers involving black holes or neutron stars – dense, heavy objects that come together in a fraction of a second.

The characteristics of the waves reveal the masses of the merging objects. They also reveal how the objects were spinning, and how they were orbiting before the merger. And those details provide hints to the existence of third-generation black holes.

One example was discovered in late 2024. A black hole about 20 times the mass of the Sun merged with one about six times the Sun’s mass. Scientists determined that the heavier black hole probably formed from an earlier merger. They even calculated the details of those black holes: about 7 and 13 times the mass of the Sun.

Third-generation black holes probably form in places where lots of black holes are jammed close together, such as the hearts of star clusters. That keeps a merged black hole from escaping – setting up the possibility of more mergers ahead.

Script by Damond Benningfield

The Moon charges at the Pleiades late tonight. As seen from most of the United States, it will pass especially close to the star cluster – either just skimming its edge or briefly covering some of its stars.

The cluster is home to more than a thousand stars of all varieties. The ones that are visible to the eye alone are especially big, hot, and bright. But they’re greatly outnumbered by stars that are much smaller, cooler, and fainter. Many of the stars belong to systems of two stars or more. And the cluster also hosts many “brown dwarfs” – objects that are more massive than planets, but not heavy enough to shine as true stars.

Over the decades, there’s been a lively debate about the distance to the cluster. Different telescopes and techniques have provided measurements that vary by many light-years. The best current number puts the distance at about 440 light-years.

But that’s the distance to the center of the Pleiades. The cluster actually spans several dozen light-years in all directions. So as you look at the cluster, the light you see from the stars that are closest to Earth headed our way dozens of years earlier than the light from the stars that are farthest – an out-of-sync view of a well-known star cluster.

The cluster’s brightest stars form a tiny dipper shape, although it’ll be tough to make out through the moonlight. The cluster will be especially close to the Moon at dawn.

Script by Damond Benningfield