NGC 4258, the first galaxy whose distance was measured using the maser technique in 2000. The latest galaxy measured by the technique is seven times more distant and is a step towards providing astronomers with a new estimate of the expansion rate of the universe.
Credit: X-ray: NASA/CXC/Univ. of Maryland/A.S. Wilson et al.; Optical: Pal.Obs. DSS; IR: NASA/JPL-Caltech; VLA: NRAO/AUI/NSF
SYDNEY: Extremely accurate measurements of ‘megamasers’ – powerful natural amplifiers of radio waves that operate similar to the way lasers amplify light – will extend the cosmic distance scale and help astronomers understand the nature of dark energy.
Masers (an acronym for Microwave Amplification by Stimulated Emission of Radiation) are sources that amplify or generate microwaves. They phenomenon occurs naturally in molecular clouds, stellar or planetary atmospheres and the accretion disk where matter falls into black holes.
The Megamaser Cosmology Project is an ambitious new attempt to measure the distance to masers in far-off galaxies. Astrophysicist James Braatz, from the U.S. National Radio Astronomy Observatory in Charlottesville, Virginia, reported on how the project is progressing at a meeting of the American Astronomical Society in Pasadena, California on Tuesday.
Cosmic distance scale
Braatz and his team have measured the angular distance and thickness of a disk of material orbiting a black hole in the centre of UGC 3789, a galaxy about 160 million light-years away.
So-called water masers in the disk amplify the radio waves from matter falling into the black hole. The radio waves were measured using the National Science Foundation’s Very Long Baseline Array and Robert C. Byrd Green Bank Telescope, as well as the Effelsberg Radio Telescope of the Max Planck Institute for Radioastronomy in Germany.
The result will extend the cosmic distance scale – the way we accurately measure distances across the universe – currently based on so-called ‘standard candles’ in astronomy, such as Type Ia supernova or Cepheid variable stars.
Hubble constant
“Measuring precise distances is one of the oldest problems in astronomy, and applying a relatively new radio-astronomy technique to this old problem is vital to solving one of the greatest challenges of 21st century astrophysics,” said Mark Reid a team member at the Harvard-Smithsonian Centre for Astrophysics in Boston, Massachusetts.
Though it will require the measurement of many more galaxies using the maser method, the project also aims to come up with an independent and very accurate value for the Hubble constant.
First discovered by Edwin Hubble in the 1920s, the Hubble constant indicates the rate at which the universe is expanding.
Hubble put the value of the expansion rate at 500 kilometers/second/megaparsec (a megaparsec is equal to about 3.26 million light years); current estimates put the value at 74.2 km/sec/Mpc, give or take 3.6 km/sec/Mpc.
