Tom Burns: A dark lane of dust and gas

Tom Burns - Stargazing

“Earth to earth, ashes to ashes, dust to dust; in sure and certain hope of the Resurrection unto eternal life.”

— The Book of Common Prayer

When we look into space past our island universe, the Milky Way galaxy and its 300 billion stars, we see other galaxies. At their centers, in their hearts as it were, we see not blazing stars, but dust.

Our own galaxy is rife with dust lanes cutting across it. This summer, look high in the sky for the constellation Cygnus. Bisecting it is a dark void that astronomers have dubbed “The Great Rift.” But the GR is not a void at all. You are seeing an enormous collection of dark dust unilluminated by any nearby starlight.

We see the same when we look at our Earth and at ourselves. We are made up of the debris from stars that died, and nothing reveals it better than a close look at a galaxy much like our own — the Sombrero Galaxy in the constellation Virgo.

Committed astronerds usually refer to it as M104, its number in the Messier catalog of such “deep-sky” objects. Careful readers will recognize the number. A couple of weeks ago, we described Vesto Slipher’s study of M104 and how it fundamentally changed our view of the cosmos. In other words, it’s worth a look, so let’s grab a star map and find it. I’ll wait while you go find yours.

Ready? 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.

In a small telescope, M104 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 there is a matching bulge on the other side of the galaxy.

You are seeing a galaxy from its edge. Seen face on, the typical galaxy looks a lot like a child’s pinwheel – a dense central core 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 large central bulge. Our own Milky Way galaxy would look about the same if we saw it from its edge and from very far away.

But our galaxy is made up of a mere 300 billion stars like our sun. The Sombrero has enough stellar material to make 1.3 trillion suns.

The Sombrero also is larger in volume. Our Milky Way measures about 600 quadrillion miles from edge to edge (that’s a 6 with 17 zeros after it). The Sombrero is 780 quadrillion miles in diameter.

The study of the Sombrero during the early 20th century revolutionized our view of the universe. When astronomers like Vesto Slipher studied M104 and galaxies like it, they discovered that these “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 one side seemed to be receding from us faster than the other side. That fact led scientists to believe that galaxies are 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 probably spinning much more slowly.

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. It is composed of the galactic detritus that has not condensed into stars.

Such dust makes up only a few percent of the galaxy’s material. We can only see it when it is silhouetted against the background stars and when we look at the galaxy “edge on” through its thickest section.

This interstellar debris comes from two sources. The first consists of hydrogen and helium molecules practically as old as the universe. The second is gas and heavier elements like carbon and iron that have been ejected from dying stars.

In fact, the only way a planet like our Earth can be created is from materials created in the incredible density and heat of a dying star. Thus, stars, like the sun and the planets that surround it, are at least second generation. They are formed in part out of the remnants of stars that lived out their long lives and came to a cataclysmic end.

This is the unalterable fate of stars – the fate of our sun and our fate as well. But out of the death of stars come the building blocks of new planets like our Earth and the substance of new life.

Ashes to ashes, dust to dust. You’d better believe it.


Today, I’m up on the dam embankment at Delaware State Park until 2:45 p.m., observing the transit of Mercury across the face of the sun. If you happen to see these words before then and you can slip away from school or work, feel free to come and take a look through my solar-safe telescope.

Tom Burns


Tom Burns is director of the Perkins Observatory in Delaware.

Tom Burns is director of the Perkins Observatory in Delaware.