Sombrero Galaxy changed view of universe

By Tom Burns


When we look into space past our Milky Way galaxy and its 300 billion stars, we see other galaxies. And across their midsections, we see not blazing stars but dust.

We see the same when we look at Earth and at ourselves. We are made up of the debris from stars that died. Nothing reveals it better than a close look at the Sombrero Galaxy in the constellation Virgo.

Before midnight in the spring, Virgo sits low on the southern horizon. It looks like a “Y” tilted to the right. The Sombrero lies about midway between the stars of Virgo and the constellation Corvus, the Crow. It is marked as M104 on most star charts.

In a small telescope, it looks like the Mexican hat for which it is named. It is long and narrow with a central bulge that juts upward.

In a larger telescope, you can see a matching bulge on the other side of the galaxy.

You are seeing a galaxy from its edge. Seen face-on, a typical spiral galaxy looks a lot like a child’s pinwheel — a dense central bulge surrounded by spiral arms of stars.

If you tilt the pinwheel so that you see it from its edge, it looks like a lens with a prominent central bulge.

The study of the Sombrero early this century revolutionized our view of the universe.

When astronomers studied galaxies like the Sombrero, they discovered that these “spiral nebulae,” as they were called then, were not part of the Milky Way but were great distances away.

The galaxies also are moving away from us at tremendous speeds. The Sombrero is rushing away at 700 miles a second.

Another startling discovery about the Sombrero was that it was slowly rotating.

It takes a star at the edge of the Sombrero 25 million years to make one circuit around the galaxy. Our Milky Way is spinning much more slowly.

Astronomers long assumed that the Sombrero was a spiral galaxy like the Milky Way, albeit with a larger central bulge.

Images by the Hubble Space Telescope reveal that its central bulge extends nearly across the galaxy. Also, the galaxy’s central black hole is unbelievably massive — the equivalent of one billion solar masses. By comparison, the Milky Way has a relatively puny central black hole of 4.5 million solar masses.

Astronomers now suspect that M 104 is not a spiral galaxy at all. Instead, it is an egg-shaped elliptical galaxy, its shape the result of two or more galaxies merging.

But what is most surprising about the Sombrero is its dark lane of dust and gas, which runs lengthwise across the entire diameter of the galaxy.

That interstellar debris ring comes from two sources. The first consists of hydrogen and helium molecules almost as old as the universe. That gas has not developed — and may never develop — into stars.

The second is gas and heavier elements like carbon and iron ejected from dying stars. The only way nature can create planets like our Earth is through the incredible density and heat of a dying star. That iron is in your blood. That calcium is in your bones.

Thus, stars like the sun and the planets surrounding it are formed in part out of the remnants of supermassive stars that lived out their short 100-million-year lives and came to a cataclysmic end.

Our sun will live much longer and die a far gentler death, but it will certainly die. That is the unalterable fate of stars — the fate of our sun and our fate as well.

But out of the death of stars comes the building blocks of new planets like Earth and the substance of new life.

Ashes to ashes, dust to dust. I will leave the discussion of eternality to theologians, who understand its principles far better than I. But it comforts me to know that my physical substance will voyage through the universe for a very long time.

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