Lonely Stars, Lonely Planets

Lonely Stars, Lonely Planets

The stars are lonely. They may be surrounded by planets, but these worldlets are rocky and lifeless, they are planetary systems frozen at some early stage at their evolution. Perhaps, many stars have planetary systems rather like our own: at the periphery, great gaseous ringed planets and cold icy moons. And nearer to the center, small, warm, blue-white, cloud-covered worlds, surrounded by an infinite grey and violet silence.

On some of these lonely planets, intelligent life may have evolved, reworking the planetary surface in some massif engineering enterprise. These worlds, if they do exist, they are our brothers and sisters in the Cosmos.

The Milky Way contains some 400 billion stars of all sorts moving with a complex and orderly grace. And all of these brilliant and enormous bundles of fire are lonely, very lonely.

Loneliness versus solitude. Image: © Megan Jorgensen (Elena)

Island in Space

Island in space

Each star system is an island in space

Our overwhelming impression, even between the spiral arms, is of stars streaming by us – a vast array of exquisitely self-luminous stars, some as flimsy as a soap bubble and so large that they could contain ten thousand Suns or trillion Earths. Others are the size of a small town and a hundred trillion times denser than lead.

Some stars are solitary, like the Sun. Most have companions and their systems are commonly double, two stars orbiting one another. But there is a continuous gradation from triple systems through loose clusters of a few dozen stars to the great globular clusters, resplendent with a million suns. Some double stars are so close that they touch, and starstuff flows between them. Most are separated as Jupiter is from the Sun.

Each star system is a lonely island in space and we grow up in isolation. Image : © Megan Jorgensen (Elena)

Can We Fall Into the Sky?

Can We Fall Into the Sky?

Black holes couldn’t have resulted from stellar collapse, from the normal evolution of massive star systems, because they were too small. Maybe they were primordial, left over from the Big Bang, captured by some unimaginable starship and towed to their destinated stations. Or maybe they were made from scratch.

There is a disk of glowing hydrogen rotating about the center of the Galaxy, and within it a ring of molecular clouds rushing outward toward the periphery of the Milky Way. You can see the ordered motions in the giant molecular cloud complex Sagittarius B2, which had for decades been a favourite hunting ground for complex organic molecules by radio-astronomical experts on Earth. Closer to the center, another giant molecular cloud is located, and then Sagittarius A West, an intense radio source.

And just adjacent at the very center of the Galaxy, locked in a passionate gravitational embrace, is a pair of immense black holes. The mass of one of them is five millions suns. Rivers of gas the size of solar systems are pouring down its mow.

Illustration: Elena

These two colossal, two supermassive black holes are orbiting one another at the center of the Galaxy.

In one second Cygnus A produces more energy than the Sun does in 40,000 years. Two enormous jets of gas, fleeing apart at almost the speed of light, are making a complex web of Rankine-Hugoniot shock fronts with the thin intergalactic gas – and producing in the process a radio beacon that shone brightly over most of the universe. All the matter in this enormous structure, 500,000 light-years across, was pouring out of a tiny, almost inconspicuous point in space exactly midway between the jets.

Bata Shoe Museum. I half-remember one summer’s night, when I was a girl. I had feared I would fall into the sky. (Quotations from M. Jorgensen). Image : © Megan Jorgensen (Elena)

Well-Mannered Galaxies

Well-Mannered Galaxies

Even a galaxy so seemingly well-mannered as the Milky Way has its stirrings and its dances. Radio observations show two enormous clouds of hydrogen gas, enough to make millions of suns, plummeting out from the galactic core, as if a mild explosion happened there every now and then.

A high-energy astronomical observatory in Earth orbit has found the galactic core to be a strong source of a particular gamma ray spectral line, consistent with the idea that a massive black hole is hidden there. Galaxies like the Milky Way may represent the staid middle age in a continuous evolutionary sequence, which encompasses, in their violent adolescence, quasars and exploding galaxies: because the quasars are so distant, we see them in their youth, as they were billions of years ago.

The stars of Milky Way move with systematic grace. Globular clusters plunge through the galactic plane and out the other side, where they slow, reverse and hurtle back again. If we could follow the motion of individual stars bobbing about the galactic plane, they would resemble a froth of popcorn. We have never seen a galaxy change its form significantly only because it takes so long to move.

The stars of Milky Way move with systematic grace, but the spiral pattern persists. Image : A Blue and Nuances Swirl by © Elena

The Milky Was rotates once every quarter billion years. If we were to speed the rotation, we would see that the Galaxy is a dynamic, almost organic entity, in some ways resembling a multy-cellular organism. Any astronomical photograph of a galaxy is merely a shapshot of one stage in its ponderous motion and evolution (but this is not quite true. The near side of a galaxy is tens of thousands of light-years closer to us than the far side; thus we see the front as it was tens of thousands of years before the back. But typical events in galactic dynamics occupy tens of millions of years, so the error in thinking of an image of a galaxy as frozen in one moment of time is small).

The inner region of a galaxy rotates as a solid body. But beyond that, like the planets around the Sun following Kepler’s third law, the outer provinces rotate progressively more slowly.

The arms have a tendency to wind up around the core in an ever-thightening spiral, and gas and dust accumulate in spiral patters of greater density, which are in turn the locales for the formation of young, hot, bright stars, the stars that outline the spiral arms. These stars shine for ten millions years or so, a period corresponding to only 5 percent of a galactic rotation. But as the stars that outline a spiral arm burn out, new stars and their associated nebulae are formed just behind them, and the spiral pattern persists. The stars that outline the arms do not survive even a single galactic rotation; only the spiral pattern remains.

Mysterious Quasars

Mysterious Quasars

The Word “quasar” is acronym for “quasi-stellar radio source”. After it became clear that not all of them were powerful radio sources, they were called QSO’s (for “quasi-stellar objects”). Because they are star-like in appearance, they were naturally thought to be stars within our own galaxy. But spectroscopic observations of their red shift show them likely to be immense distances away.

The quasars seem to partake vigorously in the expansion of the universe, some receding from us at more than 90 percent the speed of light. If they are very far, they must be intrinsically extremely bright to be visible over such distances; some are as bright as a thousand supernovae exploding at once.

In considering the quasars, we confront profound mysteries. Image: © Elena

Just as for Cyg X-1, their rapid fluctuations show their enormous brightness to be confined to a very small volume, in this case less than the size of the solar system. Some remarkable process must be responsible for the vast outpouring of energy in a quasar. Among the proposed explanations are the following: 

1) quasars are monster versions of pulsars, with a rapidly rotating supermassive core connected to a strong magnetic field; 2) quasars are due to multiple collisions of millions of stars densely packed into the galactic core, tearing away the outer layers and exposing to full view the billion-degree temperatures of the interiors of massive stars; 3) quasars are galaxies in which the stars are so densely packed that a supernova explosion in one will rip away the outer layers of another and make it a supernova, producing a stellar chain reaction; 4) quasars are powered by the violent mutual annihilation of matter and antimatter preserved in the quasar until now; 5) a quasar is the energy released when gas and dust and stars fall into an immense black hole in the core of such a galaxy, perhaps itself the product of ages of collision and coalescence of smaller black holes; 6) quasars are “white holes”, the other side of black holes, a funneling and eventual emergence into view of matter pouring into a multitude of black holes in other parts of the universe, or even in other universes.

Whatever the cause of a quasar explosion, one thing seems clear: such a violent event must produce untold havoc. In every quasar explosion millions of worlds – some with life and the intelligence to understand what is happening – may be utterly destroyed.

The study of galaxies reveals a universal order and beauty, but it also shows us chaotic violence on a scale hitherto undreamed of. That we live in a universe which permits life is remarkable. That we live in one which destroys galaxies and stars and worlds is also remarkable. The universe seems neither benign nor hostile, merely indifferent to the concerns of such puny creatures we are.