Milky Way discoveries fuel7 astronomers’ imaginations

Press, 31 January 1986, Page 22

Milky Way discoveries fuel 7 astronomers’ imaginations

By

SANDRA BLAKESLEE

NZPA-NYT Los Angeles Strange new objects have been found at the centre of the Milky Way galaxy, giving rise to wild and wonderful theories that astronomers concoct to explain the unexplained. ; . Two discoveries, reported in astronomy journals, have provided new fuel for astronomers’ imaginations. First, there is evidence that our galaxy possesses a jet of extremely hot gas streaming out of its nucleus. Such a jet slipports the theory that: a black hole — a concentration of matter so dense that even light cannot escape its gravity — lies at the heart of the Milky Way. Second, three threadlike structures have been found cutting across : the central region of 'the galaxy. They are enormous — more than 100 light years long by one light year wide — almost straight lines of radio emission. They are' not clearly linked to 1 any other structures, such as the giant arc of parallel, luminous filaments' recorded earlier by: the same project. The new discoveries are far more threadlike.

“These threads' are unique,” said Mr George

Field, an astronomer of the Harvard-Smithsonian Centre for Atrophysics in Cambridge, Massachusetts. He said they might be evidence for objects called cosmic strings which, according to some cosmological theories, are remnants from the birth of the universe. The threads have been mapped by Professor Mark Morris, of the University of California, at Los Angeles, and a former graduate student, Mr Farhad Yusef-Zadeh, now of the astronomy department at Columbia University.

The “Astronomical Journal” carries a report of the discovery, which was made at the Very Large Array, a radio-tele-scope in Socorro, New Mexico. The gas jet was discovered by Professor Morris and Mr Yusef-Za-deh in collaboration with' two Australian astronomers, Mr O. B. Slee and Mr G. J. Nelson, using the Culgoora radioheliograph in Australia.

The objects described by these astronomers join a growing list of newly discovered phenomena at the centre of the Milky Way.

All have been discovered with the V.L.A. and other radio-telescopes, as well as through observations made at infra-red wavelengths, rather than with visible light.

Optical telescopes cannot "see” into the centre of the galaxy because it is shrouded with thick, interstellar dust Radio and infra-red waves, however, do penetrate the dust and can be converted into visual images. Radio-telescopes have thus far identified a small, very intense source of radiation at the core of the Milky Way. This is surrounded by spiralshaped features, which appear to be gases circling towards the centre, like bath water falling into a drain. Outside this is more material that forms a spiral around the central core. Nearby are shellshaped objects, which may be remnants of exploded stars.

Further out are enormous arched loops of material that may represent a gigantic magnetic field connected to the galaxy’s core. There are also two cone-shaped objects that have not yet been explained.

To this picture are now added the unexplained threads, and the gas jet.

Of the two findings, Professor Morris said, the jet was more understandable. Very active galaxies were known to shoot jets of extremely hot matter deep into space, he said.

Such jets appeared as

enormous blobs of radio emission stemming from opposite sides of the galaxy, and they’? were connected to the central core of galaxies. Theorists said such jets were generated by enormous black holes at the centre of galaxies, Professor Morris said.

Because the Milky Way was a quiet galaxy, it was suprising to find evidence of a gas jet. “But it is not impossible that we have such a jet,” he said. “Our galaxy may be different from the more energetic ones only in degrees. In our galaxy the volume may be turned down.” The threads, on the other hand, were a brand new, completely different observation. They were remarkably constant, Professor Morris said.

"It is a real surprise to see something so large and so ordered. It is very tumultuous in the centre of the galaxy. It should not be too long before super-novas or other events should begin to tear something like these threads apart. Yet there they are.” Professor Morris said it was easier to say what the threads were not. They could not be shock waves, for example, because their edges were too uniform. Shock waves would show more disorder.

They were probably not gas jets, he said, because

they could not be connected with any source. It was unlikely that they represented the wake of some object moving through the galaxy, because they did not curve in a way to show that, he said. <

Another possible explanation was that they were like the magnetic flux tubes seen on the sun. Such tubes channel very hot gases and emit radio waves. However, if the threads were flux tubes, they would have to , be connected to some source. “Where are they anchored in the galaxy?” Professor Morris asked. “They do not connect up • to anything we’ve ever seen before.” Mr Field, the Harvard astronomer, ventures that the threads may .be cosmic strings. Strings are defects in the fabric of space left over from the “Big Bang” he said, referring to the widely held theory about a vast explosion from which the universe, as we know it, evolved.

"Of course, all this is very speculative. But I’ve been looking at radio waves all my life. Most make sense. They tend to be jets or shock waves and they fit known phenomena. But a long, slender, uniformly bright object strikes me as the most extraordinary thing I’ve ever seen.”