Cosmic Times

Cosmic Times

Age of the universe:
Size of the universe:
300,000 light years

Mt. Wilson Astronomer Estimates Milky Way Ten Times Bigger than Thought

But Disputes Suggestions That Spiral Nebulae are Other ‘Island Universes'

Photo of Harlow Shapley

Image credit: AIP Emilio Segre Visual Archives, Shapley Collection

Photo of Harlow Shapley in his office at Harvard circa 1935.

The Milky Way is a "discoidal" (disc-shaped) galaxy of stars 10 times bigger than astronomers have previously thought, according to Mt. Wilson astronomer Dr. Harlow Shapley. He also claims the Sun is located closer to the edge of the disc than the center. However, he disagrees with the hypotheses of other astronomers that claim dozens of other spiral nebulae observed in the skies are other galaxies or "island universes" that resemble the Milky Way.

Dr. Shapley astonished astronomers last year and this year when he published a total of 26 scientific papers in several astronomical journals. In these papers, Dr. Shapley examined other recent astronomical work in amazing detail. He also published the results of his own astronomical photography using the 60-inch reflector of the Mount Wilson Observatory in southern California. His favorite subject of study was globular star clusters which are nearly spherical clusters of hundreds of stars. These clusters have puzzled astronomers for years because they are located in peculiar positions in only certain parts of the sky. In his study, Dr. Shapley discovered 17 new globular star clusters.

In addition to pinpointing the exact position of each globular cluster in the sky, he also analyzed their light using a spectroscope to determine if they were approaching the Sun or moving away from it. From this analysis he calculated the gravitational forces acting on the clusters. He also tried to determine if they were revolving around any common center and where that common center was located. Furthermore, he calculated the distances of the globular clusters from the Sun using Cepheid variable stars. This new method of measuring distance was discovered by Miss Henrietta Leavitt of Harvard Observatory.

After years of diligent study, often assisted by his wife Martha B. Shapley, Dr. Shapley has published a number of astonishing conclusions.

Dr. Shapley concluded that our galactic universe is a single, enormous unit, the size and form of which is shown by the widely scattered globular clusters. Dr. Shapley added that the center of our discoidal galaxy is more than 60,000 light- years away in the direction of the constellation Sagittarius.

His conclusions contradict generally accepted astronomical wisdom. Until last year, most astronomers believed that the Sun was near the center of our galaxy, and that the radius of the galaxy was about 3000 light years. Some astronomers thought the galactic system might be as large as 10,000 to 20,000 light-years across. According to Dr. Shapley, the positions of globular clusters in the galaxy indicate that the actual diameter of the galactic system is about 300,000 light-years across. This is more than 10 times larger than any other astronomer had hypothesized.

Dr. Shapley said that this newer concept rules out the possibility that other spiral nebulae would be groups of stars of a size comparable to the Milky Way. Such a huge size would mean these spirals were inconceivable distances away in space. As an example, he pointed out that if a bright spiral of 10' (0.17° in angular measure) diameter has an actual diameter comparable to that of the Milky Way, its distance must be greater than 100 million light-years, and its measured rotational speed would exceed the speed of light.

In short, Dr. Shapley concludes, many observations "all seem definitely to oppose the 'island universe' hypothesis of the spiral nebulae." •

A service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA/GSFC