H1821+643
Credit
Illustration: Springel et al. (2005); Spectrum: NASA/CXC/CfA/Kovács et al.
New results from NASA's Chandra X-ray Observatory may have helped
solve the Universe's "missing mass" problem, as reported in our latest press release. Astronomers cannot account for about a third of the normal matter — that is, hydrogen, helium, and other elements — that were created in the first billion years or so after the Big Bang.
Scientists have proposed that the missing mass could be hidden in
gigantic strands or filaments of warm (temperature less than 100,000
Kelvin) and hot (temperature greater than 100,000 K) gas in
intergalactic space. These filaments are known by astronomers as the
"warm-hot intergalactic medium" or WHIM. They are invisible to optical light
telescopes, but some of the warm gas in filaments has been detected in
ultraviolet light. The main part of this graphic is from the Millenium
simulation, which uses supercomputers to formulate how the key
components of the Universe, including the WHIM, would have evolved over
cosmic time.
If these filaments exist, they could absorb certain types of light such as X-rays
that pass through them. The inset in this graphic represents some of
the X-ray data collected by Chandra from a distant, rapidly-growing
supermassive black hole known as a quasar.
The plot is a spectrum — the amount of X-rays over a range of
wavelengths — from a new study of the quasar H1821+643 that is located
about 3.4 billion light years from Earth.
The latest result uses a new technique that both hones the search for
the WHIM carefully and boosts the relatively weak absorption signature
by combining different parts of the spectrum to find a valid signal.
With this technique, researchers identified 17 possible filaments lying
between the quasar and Earth, and obtained their distances.
Light Path
Credit: NASA/CXC/K. Williamson, Springel et al.
For each filament the spectrum was shifted in wavelength to remove
the effects of cosmic expansion, and then the spectra of all the
filaments were added together so that the resulting spectrum has a much
stronger signal from absorption by the WHIM than in the individual
spectra.
Indeed, the team did not find absorption in the individual spectra.
But by adding them together, they turned a 5.5-day-long observation into
the equivalent of almost 100 days' worth (about 8 million seconds) of
data. This revealed an absorption line from oxygen expected to be
present in a gas with a temperature of about one million Kelvin.
By extrapolating from these observations of oxygen to the full set of
elements, and from the observed region to the local Universe, the
researchers report they can account for the complete amount of missing
matter.
A paper describing these results was published in The Astrophysical Journal on February 13, 2019, and is available online at https://arxiv.org/abs/1812.04625.
The authors of the paper are Orsolya Kovács, Akos Bogdan, Randall
Smith, Ralph Kraft, and William Forman all from the Center for
Astrophysics | Harvard & Smithsonian in Cambridge, Mass.
NASA's Marshall Space Flight Center in Huntsville, Alabama, manages
the Chandra program for NASA's Science Mission Directorate in
Washington. The Smithsonian Astrophysical Observatory in Cambridge,
Massachusetts, controls Chandra's science and flight operations.
Fast Facts for WHIM: H1821+643:
Category: Quasars & Active Galaxies, Cosmology/Deep Fields/X-ray Background
Constellation: Draco
Observation Date: 4 observations during Jan 17-24, 2001
Observation Time: 130 hours 33 minutes (5 days 10 hours 33 minutes )
Obs. ID: 2186, 2310, 2311, 2418
Instrument: ACIS
References: Kovács O. et al., 2019, ApJ (in press); arXiv:1812.04625
Distance Estimate: About 3.4 billion light years
Source: NASA’s Chandra X-ray Observatory
