Halton Arp

Halton Christian "Chip" Arp (March 21, 1927 – December 28, 2013) was an American astronomer.

Arp was born on March 21, 1927, in New York City.

He was married three times, has four daughters and five grandchildren.

His bachelor's degree was awarded by Harvard (1949), and his PhD by Caltech (1953).

During the 1950s bright radio sources, now known as quasars, had been discovered that did not appear to have an optical counterpart.

Afterward he became a Fellow of the Carnegie Institution of Washington in 1953, performing research at the Mount Wilson Observatory and Palomar Observatory.

Arp became a research assistant at Indiana University in 1955, and then in 1957 became a staff member at Palomar Observatory, where he worked for 29 years.

In 1960 one of these sources, 3C 48, was found to be associated with what appeared to be a small blue star.

When the spectrum of the star was measured, it contained unidentifiable spectral lines that defied all attempts at explanation; John Gatenby Bolton's suggestion that these were highly redshifted sources was not widely accepted.

In 1963 Maarten Schmidt found a visible companion to the quasar 3C 273.

Using the Hale telescope, Schmidt found the same odd spectra, but was able to demonstrate that it could be explained as the spectrum of hydrogen, shifted by a very large 15.8% If this was due to the physical motion of the "star", it would represent a speed of 47,000 km/s, far beyond the speed of any known star and defying an obvious explanation.

Schmidt noted that redshift is also associated with the expansion of the universe, as codified in Hubble's law.

If the measured redshift was due to expansion, then the object in question would have to be very far away, and therefore have an extraordinarily high luminosity, equally beyond any object seen to date.

This extreme luminosity would also explain the large radio signal.

Schmidt concluded quasars are very distant, very luminous objects.

Schmidt's explanation for the high redshift was not universally accepted at the time.

Another explanation that was offered was that it was gravitational redshift that was being measured.

Several other mechanisms were proposed as well, each with their own problems.

He was known for his 1966 book Atlas of Peculiar Galaxies, which documented peculiarities among galaxies.

Arp was also known as a critic of the Big Bang theory and for advocating a non-standard cosmology incorporating intrinsic redshift.

Arp compiled a catalog of unusual galaxies titled Atlas of Peculiar Galaxies, which was first published in 1966.

Arp realized that astronomers understood little about how galaxies change over time, which led him to work on this project.

This atlas was intended to provide images that would give astronomers data from which they could study the evolution of galaxies.

Arp later used the atlas as evidence in his debate on quasi-stellar objects (QSOs).

Other astronomers now recognize Arp's atlas as an excellent compilation of interacting and merging galaxies.

Many objects in the atlas are referred to primarily by their Arp number.

Many of these objects (particularly Arp 220) are also used as spectral templates for studying high-redshift galaxies.

Arp himself disputed the idea that the peculiar galaxies were merging, claiming, rather, that apparent associations were prime examples of ejections from a host galaxy.

In 1966, Arp published the Atlas of Peculiar Galaxies, which contained photographs of 338 nearby galaxies that did not fall into any of the classic categories of galaxy shapes.

His goal was to produce a selection that modellers could use in order to test theories of galactic formation.

By testing against the collection, one could quickly see how well a particular theory stood up.

One group of these, numbers 1 through 101, were otherwise conventional galaxies that appeared to have small companion objects of unknown origin.

In 1967 Arp noted that several of these objects appeared on the list of quasars.

In some photographs a quasar is in the foreground of known galaxies, and in others there appeared to be matter bridging the two objects, implying they are very close in space.

If they are, and the redshifts were due to Hubble expansion, then both objects should have similar redshifts.

The galaxies had much smaller redshifts than the quasars.

In 1983 he was disbarred from US telescopes due in part to his unorthodox theories, so he joined the staff of the Max Planck Institute for Astrophysics in Germany.

Arp published Seeing Red: Redshift, Cosmology and Academic Science in 1998.

He died in Munich, Germany on December 28, 2013.

He was an atheist.