Explosions In The Milky Way

Press, Volume CVI, Issue 31143, 20 August 1966, Page 12

Explosions In The Milky Way

[By

ROBERT COWEN

tn the

Science Monitor/’J

PLOUDS of hydrogen gas moving swiftly toward the earth are yet another indication that the centre of the Milky Way Galaxy may be rocked by violent explosions. A research team at Ohio State University Radio Observatory detected the gas clouds by the radio noise they emit. This noise has a wave length of 21 cen- : timetres which is char- ; acteristic for hydrogen. In reporting this to a recent I meeting of the American i Astronomical Society, the [Ohio State radio astronomers i said they did not yet know I how dense the clouds are or 'how far away they lie. But analysis of their radio noise shows they are moving toward the earth at speeds of up to 500.000 miles an hour. Flattened Footballs The Ohio team includes Dr J. D. Kraus, observatory director; Dr D. S. Mathewson, visiting professor from Mount Stromlo Observatory in New South Wales, Australia: S. Y. Meng, a research assistant; and W. D. Brundage, a graduate student. Dr Kraus says that, while no-one really knows where the clouds come from, they may have been thrown out by an explosion in the core of our galaxy. In this case, their outward rush has been checkled by the gravitational pull of the galaxy. They now are Amoving inward toward the I galaxy rather than avzaj- from it. This would be in keeping with recent ideas on the nature of galaxies. Some types of galaxies j range in shape from spheres to flattened footballs. These are the elliptical galaxies. Like Pinwheels Others, including our own galaxy, belong to the family of the spirals. These galaxies have bright central regions but of which spiral more or less well-defined arms of gas. dust, and stars. They look a little like pinwheels. Seen edge-on they are like dies with a central bulge.

In our Milky Way Galaxy the disc is about 100,000 light years across while the central nucleus is about 1000 light years thick. A light year, the distance light travels in a year, is 6,000.000,000,000. Halo Of Gas

This vast Milky Way system contains an estimated 100 billion stars plus masses of dust and gas. It is also thought to be surrounded by a halo of very thin gas with a scattering of stars and star clusters. The sun and its planets are in one of the spiral arms. They lie close to the central plane of the galactic disc but are 25,000 to 30,000 light years from the centre. Since the galaxy is believed to be rotating, the solar system moves around centre. Astronomers think it takes 200 million years to make one circuit. First Theory Astronomers once thought galaxies, formed from cosmic dust and gas, were shaped largely by forces of gravity and rotation. But a decade ago, V. A. Ambartzumian, director of the Byurakan Observatory in Russia suggested that events in the Consolation QUT of sympathy for the bald head, society decided on a face-saving formula and attributed to the bald pate the gift of profound intelligence and knowledge.—A doctor in a 8.8. C. broadcast about American research into a cure for baldness.

central nuclei of galaxies mayplay a decisive role. He thought the nuclei might be seats of unknown types of energy production and even of an unknown state of matter.

Discoveries since then have greatly strengthened his suggestion. Many so-called “peculiar” galaxies have been found which show unmistakable signs of massive and probably violent release of energy. Some have jets of luminous matter shooting out of them. Many are strong sources of radio noise. Sometimes the radio noise seems to be coming from vast clouds of material that may have been ejected from the galaxy. Signs Of Violence Even “ordinary” spiral galaxies like our own, which once were thought to be quite placid, show signs of violence. Two years ago, Dr. J. H. Oort, and his colleagues at Leiden Observatory, Holland, found massive movements of hydrogen near the core of our galaxy. They may have been flung outward in a great explosion some 10 million years ago, Dr. Oort said. Speeds Recorded The Leiden astronomers reported further measurements last May at the 29th International Astronomical Union, symposium held at the Byurakan Observatory. They have found speeds of about 450,000 miles an hour near the central region of the galaxy. They could not tell whether this was an outflow or infall of matter. But it was

four times faster than any: such motion found up to that time.

At the same conference. G.' Munch of the Mount Wilson; and Palomar Observatories ■ reported finding irregular; movements with 650 light; years of the centre of the Andromeda Nebula. This' spiral galaxy is 2 million light years away and is thought to be a twin of our own. More Evidence Now the Ohio State astronomers have found even morel suggestive evidence of violence at the heart of our galaxy. The gas movements seen by the Dutch are in the I plane of the galaxy and near: its centre. The gas seen by Dr. Kraus and his associates! is far out from that plane. It I is moving inward just as! though it had been flung out- ! ward explosively, perhaps! only a million years ago. Hydrogen Clouds No-one knows how such explosive energy could be generated. It is far greater than any nuclear reaction would supply. Yet violence seems to be characteristic of a galaxy’s core. The unknown processes it involves may be a key to understanding how galaxies evolve-and why they develop into different types. The in-falling hydrogen clouds found by the Ohio States astronomers are another important phenomenon that should help astronomers gain that understanding, i