StarDate

The next time you go jetting off into the universe, watch out for black holes — there are lots of them. A recent study calculated that there are 40 billion billion of them — a four followed by 19 zeroes.

The study was looking at the most common type of black hole — ones that are born from the death of a massive star. Such black holes range from a few times the mass of the Sun to more than a hundred times the Sun’s mass. Astronomers have cataloged several thousand of them, mainly in our home galaxy, the Milky Way.

Scientists in Italy simulated conditions in stars and galaxies throughout the universe. In particular, they looked at the rate at which galaxies give birth to stars, the masses of the stars, and the composition of the stars — especially the ratio of elements other than hydrogen and helium. And they considered how many black holes are born in binary systems — pairs of stars bound by their gravity.

And they found that the universe must contain many more black holes than suggested by earlier studies. In fact, this class of black holes could account for up to one percent of all the normal matter in the universe — a hundred times more than found in the giant black holes at the hearts of galaxies.

The universe is big, so there’s a lot of elbow room between black holes. But since a black hole doesn’t produce any energy on its own, one can sneak up on you — especially with 40 billion billion of them lurking in the cosmos.
 

Script by Damond Benningfield

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An old star cluster has the blues. A lot of them, in fact. Astronomers have discovered dozens of blue stars in the cluster when there shouldn’t be any at all.

Messier 67 is an old cluster — roughly four billion years old. Most clusters of its type don’t stick together that long — their stars are pulled away, and the cluster simply vanishes.

As befits an old cluster, most of the stars in M67 are fairly cool, so they shine yellow or orange. But some of the stars are blue, and that’s a bit of problem. Blue stars tend to be hot and massive, so they burn out quickly. And many of them explode. So any blue stars born in M67 should have expired billions of years ago.

Today’s blue stars probably had some help in turning blue: They stole gas from companion stars. As the gas piles up on the surface of a stellar thief, it makes the surface hotter — and that makes it bluer.

Most of the “second-chance” blue stars are known as blue stragglers. But a few are called blue lurkers. They spin much faster than expected. That was discovered only recently, so the stars have been “lurking” in plain sight. They probably spin up as the gas from a companion funnels onto them — adding to the “blues” in this old star cluster.

M67 is in Cancer, the crab, and is high in the southern sky at nightfall. Through binoculars, it looks like a hazy smudge of light — the combined light of hundreds of stars that are old — even if they don’t look it.
 

Script by Damond Benningfield

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If you want to see a lot of galaxies, you need to look up — not just up into the sky, but up and away from our own galaxy, the Milky Way. And the best spot for doing that is in and around the constellation Coma Berenices, which climbs high overhead on spring evenings. It’s the location of the north galactic pole — the spot that’s 90 degrees away from the plane of the Milky Way.

That plane outlines the disk of the Milky Way. It’s filled with stars and with clouds of gas and dust. There’s so much stuff that it’s hard to see the intergalactic space beyond.

As you look farther from the glowing band of the Milky Way, though, many more galaxies come into view. Some of them are visible through binoculars, though most of them require a telescope.

In fact, there are large clusters of galaxies in Coma Berenices and the adjoining constellation Virgo. In all, they contain several thousand galaxies. There are many other galaxies over in the opposite direction from Virgo, near the Big Dipper. HETDEX, a large project at McDonald Observatory, is looking at thousands of remote galaxies in that region to study dark energy — a force that’s causing the universe to expand faster as it ages.

Coma Berenices is low in the east at nightfall, then wheels high overhead after midnight. In early evening, the north galactic pole is to the right of the tip of the Big Dipper’s handle. Galaxies are scattered all across that region — high “above” the Milky Way.
 

Script by Damond Benningfield

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The galaxy is filled with twins — pairs of stars that travel through space together, tethered by their gravitational pull. The most impressive pair yet confirmed is in a gigantic stellar nursery. Combined, the two stars are almost 200 times the mass of the Sun.

NGC 3603 A1 is about 25,000 light-years away, in the southern constellation Carina.

Astronomers recently combed through years of observations of the system made by Hubble Space Telescope. That allowed them to determine the masses of the two stars with much greater accuracy than previous studies. The main star is 108 times the mass of the Sun, while its companion is 82 times the Sun’s mass — the heaviest binary system measured at high precision.

Their mass isn’t the only impressive thing about the stars, though. Both of them are tens of thousands of degrees hotter than the Sun. And most impressive of all, they’re more than a million times brighter than the Sun.

The stars are so close together that the bigger star is puffing out toward its companion. Before long, some of its gas should start funneling onto the companion. And that will change the evolution of both stars — although no one is quite sure how. In the end, the core of each star may collapse to form a black hole. Its outer layers may blast into space as a supernova — or they might fall back onto the black hole. So no matter how it plays out, the stars of NGC 3603 A1 have impressive futures.
 

Script by Damond Benningfield

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Two planets are staging an impressive encounter in the early morning sky. They’re quite low in the southeast at first light, not far to the upper right of Venus, the “morning star.” Mars and Saturn aren’t nearly as bright as Venus. But their proximity to it — and to each other — will help them stand out.

Mars is the fourth planet from the Sun — one spot farther than Earth. Like Earth, it’s a ball of rock and metal. It has an atmosphere, but it’s not especially inviting. The air is extremely thin and cold, and Mars has no magnetic field to protect life from radiation. Spacecraft have found that Mars was much more welcoming billions of years ago, so it could have supported life when it was younger.

There’s little hope of life on Saturn, the sixth planet from the Sun. It’s a big ball of gas with no solid surface. But some of its moons appear to have all the basic ingredients for life: water, energy, and the right chemistry. It won’t be easy to find life, though, because conditions on the moons are hostile, or because life is likely to be hidden far below the surface.

Saturn and Mars themselves are anything but hidden now. Look for them before and during dawn the next few days. Saturn is a bit brighter. Mars is to its upper right tomorrow, but will slide below Saturn in a few days. At their closest, on Monday and Tuesday, they’ll be separated by about half a degree — less than the width of your little finger held at arm’s length.
 

Script by Damond Benningfield

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Champagne and the Milky Way Galaxy have one thing in common: they’re both bubbly. The bubbles in champagne tickle the nose and the palate. The bubbles in the Milky Way tickle clouds of gas and dust, creating new stars.

Our solar system sits near the center of the Local Bubble — a cloud that’s a thousand light-years across. Its surface is bedazzled by several clusters of young stars.

In a recent study, astronomers obtained precise details about nearby young stars from Gaia, a space telescope that’s mapping more than a billion stars. They then used data visualization software to plot the locations of the stars. Catherine Zucker, a member of the team, explained what they found:

ZUCKER: In the present day, almost every single nearby young star lies on the surface of the Local Bubble. As a result, by turning back the clock and tracing the history of star formation forward to the present day, we can explain how all nearby star formation began.

The bubble began about 14 million years ago, when a star exploded as a supernova. The shockwave, along with those of other supernovas, began clearing a giant cavity.

ZUCKER: As this bubble expands, it sweeps up clouds of gas and dust on its surface sort of like a snowplow can sweep up snow.

Some of that gas and dust collapses to form new stars, including the ones measured by Gaia.

Our solar system entered the Local Bubble about five million years ago. It will remain inside it for several million years more.
 

Script by Damond Benningfield

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In the 1840s, William Parsons, the Earl of Rosse, designed and built the world’s largest telescope. Known as the Leviathan of Parsonstown, it provided especially sharp views of the heavens. That made it well suited for studying faint, fuzzy nebulae, which showed little detail through lesser instruments.

Parsons turned his giant toward M97, an object near the Big Dipper. It had been cataloged by Charles Messier, a French comet hunter. Parsons’s drawing of the object resembled an owl — a bright disk with two round voids. The object became known as the Owl Nebula — a name it retains today.

The owl’s “eyes” appear to be large, empty bubbles inside two shells of gas.

The nebula was created by a dying star that’s blowing its outer layers into space. It expelled the first shell perhaps 10,000 years ago. The second followed a few thousand years later. Later still, the star expelled a third wave. It consisted of two separate bubbles that expanded from the star’s poles. They carved dark voids in the earlier shells. Those bubbles have stopped expanding. Eventually, they may collapse and fill with gas from the shells around them — depriving the owl of its distinctive eyes.

The Owl Nebula is about 2,000 light-years away. As night falls, it’s close to the lower right of Merak, the star at the bottom outer corner of the bowl of the Big Dipper, which is in the northeast. The Owl Nebula is an easy target for small telescopes.
 

Script by Damond Benningfield

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A seagull with a hundred-light-year wingspan flies across the southwest on these early spring evenings. It’s not far from Sirius, the brightest star in the night sky.

The Seagull Nebula is a complex of several giant clouds of gas and dust. One of the clouds forms the gull’s wings, and a smaller one forms its head.

All of the clouds are stellar nurseries. They’ve given birth to thousands of stars, with many more still taking shape. Some of the stars are especially massive and hot. They produce a lot of ultraviolet light, which makes the nebula glow. The radiation zaps hydrogen gas, causing it to emit red light. And the starlight reflects off grains of dust, creating patches of blue.

Those massive stars are both helping and hindering the birth of more stars. In addition to radiation, the stars produce powerful winds of charged particles. They compress the gas and dust around them, causing some of the material to collapse and form new stars. At the same time, the radiation and particles blow some of the gas and dust away, preventing it from making stars.

The Seagull Nebula is about 3700 light-years away. It’s along the border between the constellations Canis Major, the big dog, and Monoceros, the unicorn. At nightfall, the nebula is close to the upper left of brilliant Sirius. The seagull is too faint to see with the eye alone, but it’s an easy target for binoculars and small telescopes.

We’ll talk about another cosmic bird tomorrow.
 

Script by Damond Benningfield

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A barely there crescent Moon just peeks into view during tomorrow’s dawn twilight. You need a clear horizon to spot it.

If the timing is right, though, you might see the entire lunar disk. The part that’s dark isn’t all that dark at all — it’s lit up by earthshine — sunlight reflecting from an almost-full Earth. Earth is bigger and more reflective than the Moon, so a full Earth is a few dozen times brighter than a full Moon.

But it’s not quite as bright as it used to be. A recent study found that Earth’s albedo — the measure of how much light it reflects — has dropped in recent years.

Researchers used telescopes in California to measure earthshine on the Moon from 1998 to 2017. They also measured changes in Earth’s brightness recorded by weather satellites. They found a decrease in Earth’s albedo of about half a percent over that period. Most of the change came in the last few years.

The scientists say the main culprit is a decrease in low cloud cover over the eastern Pacific Ocean — a result of Earth’s changing climate. Clouds reflect more light than the ocean does, so without them, that region has gotten darker. And that could contribute even more to climate change. Because clouds reflect a lot of sunlight, they keep the surface cooler. Without them, that region of the Pacific Ocean should absorb more solar energy — making both the ocean and the rest of the planet a little warmer.

Tomorrow: a giant seagull.
 

Script by Damond Benningfield

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One of the closest neighboring “star systems” doesn’t contain any stars at all. Instead, it’s a pair of brown dwarfs — objects that aren’t massive enough to shine as true stars, but that are too massive to be considered planets. In this case, though, both objects probably look a lot like Jupiter, the largest planet in the solar system.

Luhman 16 is just six and a half light-years away — the third-closest system to the Sun. The two brown dwarfs are so faint, though, that they weren’t discovered until 2013. Observations made since then have shown that the brown dwarfs orbit each other once every 27 years. Both are about the size of Jupiter, but roughly 30 times more massive.

They’re also a good bit hotter than Jupiter, so they produce their own light — mostly at infrared wavelengths. Yet they’re cool enough for molecules in their atmospheres to condense.

Although we can’t see them, those molecules probably form bands of clouds like those on Jupiter. Some bands are thick, so they’re dark. Others are thin, so they’re brighter. And storms may spin through the bands and around the poles — also like Jupiter. So while the brown dwarfs of Luhman 16 are unlike anything in the solar system, they’d probably look pretty familiar.

Luhman 16 is in Vela, the sails. From the southern U.S., the constellation just climbs above the southern horizon during the evening hours. Luhman 16 is too faint to see without a lot of help.
 

Script by Damond Benningfield

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