StarDate

If we could send a spacecraft to the supergiant star Antares, it could take a really close look. In fact, it’s not hard to imagine that we could build a probe that could safely plunge into the star’s outer layers. Although those layers are hot, they’re also quite thin – a fairly decent vacuum. So a probe might be able to descend millions of miles below the surface and survive.

Antares is a monster. It’s roughly a dozen times the mass of the Sun, and 700 times the Sun’s diameter. So its average density is less than one-billionth of the Sun’s. And most of its mass is concentrated deep in the core, which is where the star generates its energy.

That means the outer layers are extremely thin – so thin that it’s tough to define the surface – it blends into the background.

The surface temperature of Antares is about 6100 degrees Fahrenheit, compared to 10 thousand degrees for the Sun. We’ve already built a probe that can approach to within a few million miles of the Sun. It has a shield that can withstand temperatures of about 2500 degrees. A plunge into Antares would be hotter, but building a shield to take the heat doesn’t seem impossible – providing a way to get an up-close look at this monster star.

Antares climbs into good view by 1 or 1:30 a.m. It’s close to the lower left of the Moon as they rise, with the Moon inching closer to the star before dawn.

Script by Damond Benningfield

Eighteenth-century astronomer William Herschel described the star system Beta Monocerotis as “one of the most beautiful sights in the heavens.” It’s one of the hidden beauties of Monoceros, the unicorn. The constellation is well up in the southwestern sky in early evening. It’s wedged between brilliant Orion and the “little dog” star Procyon.

There’s not much to see in Monoceros with the eye alone. But telescopes reveal a bounty of beautiful sights. And Beta Monocerotis straddles both domains. It’s faintly visible to the unaided eye as one of the unicorn’s two brightest stars. But to see the same beauty that Herschel did, you need a telescope. That view reveals three stars, not one, all with a fetching blue-white color.

The color comes from the temperatures of the stars – their surfaces are many thousands of degrees hotter than the Sun’s. And all three stars are much more massive than the Sun. That revs up the nuclear reactions in their cores, which is what makes them so hot. It also makes the stars extremely bright – as much as 3200 times as bright as the Sun. So the stars are visible across 700 light-years of space.

The two faintest members of the system probably form a wide binary, with the third star orbiting around them. Combined, they make Beta Monocerotis a beautiful skywatching sight – a vision in blue for an early-spring night.

Script by Damond Benningfield

We never know everything there is to know about a person from the first glance – or anything else, for that matter. And that includes the stars. It takes a lot of time, and a lot of looks with different instruments, to piece together the whole story.

One example is the system Gaia BH2. It consists of two known objects. But there might once have been a third object – a star that was gobbled up.

The system was discovered by Gaia, a space telescope. It revealed two objects: a black hole about nine times as massive as the Sun, and a giant star about 1.2 times the Sun’s mass. They orbit each other once every three and a half years.

Ground-based telescopes revealed the composition of the giant. Its chemistry looked like that of an ancient star.

But observations by TESS, another space telescope, suggested otherwise. The satellite measured “starquakes” on the surface of the giant star. Sound waves bounce around inside the star and back to the surface. So just as an earthquake tells us what’s happening below the surface of Earth, a starquake tells us what’s happening deep inside a star.

The quakes revealed that the star spins faster than expected. That suggests it was spun up by interactions with something else. It might have swallowed debris that encircled the black hole. Or it might have swallowed another star, changing the chemistry at its surface – prematurely “aging” this giant star.

Script by Damond Benningfield

The stars of Spica may be headed for a breakup. One of the two stars is likely to explode as a supernova. That may send the stars careening into the galaxy on their own.

Spica is the brightest star of Virgo. It rises just above the Moon early this evening.

The system consists of two big, heavy stars. The primary star, Spica A, is about 10 times the mass of the Sun. Spica B is about seven times the Sun’s mass. The stars are so close together that they whirl around each other once every four days.

Within a few million years, Spica A will consume all the nuclear fuel in its core. The core will collapse, probably forming a neutron star – an object up to twice the mass of the Sun, but only as big as a city. Its outer layers then will blast into space at a few percent of the speed of light – a supernova.

The companion star should survive, although it might lose some gas from its surface. But what happens next is tricky.

Supernovas sometimes explode asymmetrically – the blast can be off-centered. That can give the neutron star a big kick. And the neutron star will be only a fraction as massive as the original star. That means its gravitational grip on its companion will be much weaker. The neutron star could zip off at high speed – perhaps fast enough to escape the galaxy.

And even if that doesn’t happen, the stars are likely to move farther apart – a bigger gap between these impressive stars.

Script by Damond Benningfield

Mercury is just peeking into view in the dawn sky. The little planet is in the east in the waxing twilight, and looks like a bright star. It’ll stand highest in the sky on Friday. But because of the angle at which it rises, it’s hard to spot. In fact, from much of the United States, you probably can’t see it at all. The view is best from south of about Dallas.

That difficulty illustrates how tough it’s been for scientists to study Mercury. It’s never in view for long – no more than a couple of hours before sunrise or after sunset. And it’s so low in the sky that we always see it through a thick layer of air, so the view is murky – like trying to make out the shapes of clouds from the bottom of a swimming pool.

In the late 1800s and the early 1900s, astronomers did make a few crude maps of Mercury’s surface. But there was a lot they couldn’t figure out. That included the length of the planet’s day. At first, it appeared that Mercury completed one turn on its axis in 88 Earth days – the same length as its year.

In the early 1960s, though, astronomers bounced radio waves off the surface. That work showed that a day lasts 59 Earth days. So Mercury completes three turns on its axis for every two orbits around the Sun – three days for every two years.

Again, look quite low in the east not long before sunrise for elusive little Mercury – a planet that’s been hard to get to know.

Script by Damond Benningfield