Earth’s cosmic sibling is sight to behold


By Tom Burns - Stargazing



The ringed planet Saturn is in the constellation Capricornus this season. To find it, look low on the southern horizon just after dark for a pale-yellow point of light.

To Saturn’s left is an even brighter point of light, the planet Jupiter. That’s right. Jupiter still looks like a point of light, even in binoculars, despite its nearly 90,000-mile diameter.

Distance tells us why. At about 33 light minutes away (around 380 million miles), you still might be able to see some of its four Galilean moons lined up around the planet, but you won’t see a planetary disk.

Saturn orbits the sun and is more than twice the distance of Jupiter at 840 million miles away (about 75 light minutes). Like Jupiter, Saturn is a cold ball of mostly hydrogen gas 75,000 miles wide. By comparison, Earth is an even punier 8,000 miles wide.

Its rings span over 200,000 miles, nearly the distance from Earth to its moon. But at such a great distance away, Saturn’s rings don’t resolve in binoculars. It takes a small telescope to see them.

Far to Saturn’s right is the constellation Scorpius, the Scorpion. The stars of Scorpius are, of course, distant suns. Sometimes called the Heart of the Scorpion, Antares is the brightest star in the constellation and the 15th brightest in the nighttime sky.

At over three quadrillion miles away, Antares is considerably more distant than Saturn. The sun’s light bouncing off Saturn takes about 75 minutes to get from the planet to your eyeballs. The light from Antares journeyed 550 years.

Antares is a supergiant star, an exploding ball of hydrogen generating 10,000 times the energy of our sun.

Antares’ redness is a sign that the star is simultaneously very young and very old. Astronomers estimate that Antares is a relative youngster at only 12 million years old.

An average star like our sun will percolate for about 11 billion years before its thermonuclear nuclear fires are quenched. Compared to the lifetime of our sun, Antares has barely begun.

However, Antares had also reached a premature old age. Part of the problem is its enormous mass. The star has about 17 times more starstuff than old Sol. And that’s a problem if longevity is your aim.

So much star stuff generates a considerable amount of gravitational force. Stars convert the hydrogen deep in their core to helium in the same reaction that fuels our hydrogen bombs. The reaction occurs because the hydrogen at a star’s center is compressed and heated to temperatures that reach tens of millions of degrees.

Our puny star generates enough gravity to compress hydrogen at a moderate rate. The sun has reached a respectable middle age after about five billion years. In about six billion years, it will stop exploding and collapse into a tiny white dwarf.

Antares’ enormous mass is compressing and converting hydrogen at a prodigious rate. After only 12 million years, it has reached decrepitude. In less than a million years, it will die most spectacularly.

As part of the dying process, Antares has swelled to enormous size. At around 480 million miles wide, if it replaced our sun at the center of our solar system, it would engulf Earth and reach out past the orbit of Mars.

Its distinct redness tells us that it has also cooled down considerably. Earlier, when it was a yellow star like our sun, it reached a surface temperature of something over 10,000 degrees. Antares’ redness indicates that it has cooled to just under 6,000 degrees. Like our sun, Antares will collapse when its thermonuclear fires abruptly end.

However, unlike our sun, the result will not be a white dwarf. Its core will collapse to an even smaller sphere and form a black hole or a neutron star. As it collapses, the star’s outer shell will explode away from the star in one of the most energetic events the universe offers.

If human beings are still around in a few hundred thousand years, they will be privileged to watch Antares briefly shine with a brightness that will rival the combined light of the full moon condensed to a single point. It will briefly light up the night and be visible for a day or three during full daylight.

Yet Saturn’s brightness exceeds Antares’ relatively fainter glow. Even a small telescope will show its mind-altering rings. Saturn’s brightest and largest moon, Titan, only a few thousand miles in diameter, is visible in a small ‘scope or binoculars.

In even the largest telescope on Earth, giant Antares will still look like a tiny point of light.

Distance makes all the difference, of course. You can see a mosquito much better than the Empire State Building if the mosquito sits on the tip of your nose, and the Empire State Building is in New York City.

Just to the right of Antares, you will find an island of stars called M4. It consists of about 200,000 stars packed into a relatively dense ball called a globular cluster. M4 shines with the combined energy of 40,000 of our suns. At over 450 trillion miles wide and 7,200 light-years away, it is over 13 times farther away from us than Antares.

The problem of distance strikes again. In a small telescope or binoculars, all those glorious stars taken together look like a tiny, fuzzy blob. You will begin to discern individual stars in a larger scope, but they will be exceedingly faint.

Most of the stars of M4 are almost as old as the universe. At 12.7 million years old, those stars formed long before the stars of the main disc of the Milky Way. Our star, the sun, and planet Earth had to wait 7.5 billion years before they coalesced out of the cloud of dust and gas that gave them birth.

Two of M4’s stars deserve special attention. PSR B1620−26 A and B are two thoroughly dead stars. They used up their hydrogen fuel years ago.

The “A” star collapsed to a dense ball called a neutron star. Its magnetic field generates a rapidly pulsating beacon detectable from Earth. Such stars, called pulsars, seem to pulsate rapidly as the spinning beacon rotates past Earth. Think of the beam as a dazzling lighthouse lamp turning at a startling rate of 100 rotations per second.

The “B” star is a white dwarf, the collapsed remnant of a star very much like our sun. Early in its stellar life, a Jupiter-like planet called PSR B1620-26 b formed around PSR B1620−26 B.

The two stars currently orbit each other, like your two thumbs slowly twiddling, except that one “twiddle takes 1,000 years or so. Oddly, the planet now orbits them both.

Here’s how that happened. The two stars formed at a great distance from each other. The “A” star formed near the dense center of M4. The sun-like “B” star formed near the globular cluster’s edge where there are fewer stars.

The “B” star migrated into M4’s dense core and traveled close to the “A” star, which was already a dead neutron star by that time. The neutron star captured the “A” star and its planet.

The two stars went into orbit around each other. Almost simultaneously, the planet was ejected from orbit around the “B” star and settled into orbit around both stars.

Billions of years later, the sun-like “A” star collapsed into a white dwarf as it ran out of the hydrogen that fueled its thermonuclear reaction.

The “B” star may have other planets. We have no way of detecting the smaller ones at this distance yet. One or more of those possible planets might have looked a lot like Earth a very long time ago. If life developed on those planets, it was born and died long before our sun and Earth began to form.

Only a TN (telescope nut) with considerable experience and a good imagination will begin to see the glory present in that fuzzy patch called M4.

That’s human nature. We feel the pain or joy of someone near and dear to us with much greater passion than we do the ups and downs of entire cultures far away.

The death of a relative is a crushing blow. Right now, our collective grief for the fall of Afghanistan to the terrorist Taliban and our fear for its people will eventually yield to new crises in new news cycles.

Sadly, the terrors of, say, Somalia and the genocide in Rwanda are — for many of us at least — a vague abstraction and fading memory.

Saturn is our cosmic sibling, so close we can learn to love the weird idiosyncrasy of its rings. Those rings are certainly more impressive than a fuzzy ball of 200,000 stars or its quirky stellar system and its strange planet.

Stargazing helps to alter our self-involved point of view. After all, our sister planet is, like our own, an inconsequential speck of dust compared with the glorious spectacle of a globular cluster isolated from us by the vastness of space and time.

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By Tom Burns

Stargazing

Tom Burns is the former director of the Perkins Observatory in Delaware.

Tom Burns is the former director of the Perkins Observatory in Delaware.