Explaining why the universe can be transparent

September 12, 2016 by Sean Nealon, University of California - Riverside
Reionization as illustrated by data from the Hubble and Chandra space telescopes. Credit: NASA/CXC/M.Weiss

Two papers published by an assistant professor at the University of California, Riverside and several collaborators explain why the universe has enough energy to become transparent.

The study led by Naveen Reddy, an assistant professor in the Department of Physics and Astronomy at UC Riverside, marks the first quantitative study of how the gas content within galaxies scales with the amount of interstellar dust.

This analysis shows that the gas in galaxies is like a "picket fence," where some parts of the galaxy have little gas and are directly visible, whereas other parts have lots of gas and are effectively opaque to . The findings were just published in The Astrophysical Journal.

The ionization of hydrogen is important because of its effects on how galaxies grow and evolve. A particular area of interest is assessing the contribution of different astrophysical sources, such as stars or black holes, to the budget of ionizing radiation.

Most studies suggest that faint galaxies are responsible for providing enough radiation to ionize the gas in the early history of the universe. Moreover, there is anecdotal evidence that the amount of ionizing radiation that is able to escape from galaxies depends on the amount of hydrogen within the galaxies themselves.

The research team led by Reddy developed a model that can be used to predict the amount of escaping ionizing radiation from galaxies based on straightforward measurements on how "red," or dusty, their spectra appear to be.

Alternatively, with direct measurements of the ionizing escape fraction, their model may be used to constrain the intrinsic production rate of ionizing photons at around two billion years after the Big Bang.

These practical applications of the model will be central to the interpretation of escaping radiation during the cosmic "dark ages," a topic that is bound to flourish with the coming of 30-meter telescopes, which will allow for research unfeasible today, and the James Webb Space Telescope, NASA's next orbiting observatory and the successor to the Hubble Space Telescope.

The research ties back to some 400,000 years after the Big Bang, when the universe entered the cosmic "dark ages," where galaxies and stars had yet to form amongst the dark matter, hydrogen and helium.

A few hundred million years later, the universe entered the "Epoch of Reionization," where the gravitational effects of dark matter helped hydrogen and helium coalesce into stars and . A great amount of ultraviolet radiation (photons) was released, stripping electrons from surrounding neutral environments, a process known as "cosmic reionization."

Reionization, which marks the point at which the hydrogen in the Universe became ionized, has become a major area of current research in astrophysics. Ionization made the Universe transparent to these photons, allowing the release of light from sources to travel mostly freely through the cosmos.

The data for this research was acquired through the low resolution imaging spectrograph on the W.M. Keck Observatory.

The collaborators of this research are Charles Steidel (Caltech), Max Pettini (University of Cambridge), Milan Bogosavljevic (Astronomical Observatory, Belgrade) and Alice Shapley (UCLA).

The papers are "Spectroscopic Measurements of the Far-Ultraviolet Dust Attenuation Curve at z~3" and "The Connection Between Reddening, Gas Covering Fraction, and the Escape of Ionizing Radiation at High Redshift."

Explore further: Green pea galaxy provides insights to early universe evolution

More information: Naveen A. Reddy et al. SPECTROSCOPIC MEASUREMENTS OF THE FAR-ULTRAVIOLET DUST ATTENUATION CURVE AT∼ 3, The Astrophysical Journal (2016). DOI: 10.3847/0004-637X/828/2/107

Naveen A. Reddy et al. THE CONNECTION BETWEEN REDDENING, GAS COVERING FRACTION, AND THE ESCAPE OF IONIZING RADIATION AT HIGH REDSHIFT, The Astrophysical Journal (2016). DOI: 10.3847/0004-637X/828/2/108

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13 comments

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baudrunner
1.7 / 5 (6) Sep 12, 2016
So, this is "the first quantitative study of how the gas content within galaxies scales with the amount of interstellar dust." Then the article deviates.

As I see it, the universe is transparent because one of those gases displacing its space is inert and does not participate in the propagation of photonic waves. In practical terms, the presence of Helium should be proportional to the transparency of a region under observation, because technically, then, it isn't detectable and its presence has to be inferred.
shavera
4.3 / 5 (11) Sep 12, 2016
the universe is transparent because one of those gases displacing its space is inert and does not participate in the propagation of photonic waves.


I don't know what you mean by this. One, saying 'photonic waves' is just plain weird. One usually speaks of photons or EM waves. But more importantly, no gas 'participates in the propagation of photonic waves.' That's the whole thing about electromagnetism. It exists aside and in addition to the stuff we call 'matter.'

Sure gases absorb parts of the EM spectrum, or get heated and re-emit radiation according to thermal distributions; and plasmas are a particularly peculiar kind of gas that, because of free charges, can be completely opaque or reflective to light in broad frequency bands.

But then you go into some weirdness about helium, and the point is that you *can* detect helium because it absorbs certain frequencies of light. So I have no idea what you're talking about.
wduckss
1.6 / 5 (7) Sep 13, 2016
The article passes only if we are blind.
Ionized particles we have in our system and are represented on the entire volume of the universe to the farthest point 13.7 (8) billion ly.
To of ionisation comes in a crash of waves with particles in space. Where there are sources of radiation exists ionized particles.
jsdarkdestruction
3.8 / 5 (10) Sep 13, 2016
Wduckks, your English needs significant work. Even the people who you think you are reaching with your posts (the cranks)can't understand what you are trying to say. You are therefore completely wasting your time here. It would be best if you left the English sites alone and focus on the sites from wherever you are.
tinitus
Sep 13, 2016
This comment has been removed by a moderator.
ThomasQuinn
5 / 5 (1) Sep 13, 2016
Well, in steady-state universe model no actual reason for some global reionization exists - or not? Which observational evidence for reionization we actually have?


How does your steady-state model explain redshift and the correlation between degree of redshift and distance of galaxies?
RNP
3.8 / 5 (10) Sep 13, 2016
@bscott
By which mechanism are you suggesting that magnetic fields can produce the observed redshift?
RNP
4.1 / 5 (9) Sep 13, 2016
@bschott
I'll give you a clue......... There isn't one.
tinitus
Sep 13, 2016
This comment has been removed by a moderator.
RNP
3.7 / 5 (9) Sep 13, 2016
@bschott
Forget the obfuscation, this is not about the cosmological explanation. It is about a claim that you made. Now back it up. By which mechanism are you suggesting that magnetic fields can produce the observed redshift?
wduckss
1 / 5 (3) Sep 13, 2016
@jsdarkdestruction
Thanks to the "well-meaning" advice. My "English" has collected more than 100,000 visits and thousands of comments. Probably main reason for visits is my English.
True if is matter a person little known (to discuss on the evidence and different the vision) criticize the language.
Did you known that in Sun system exists ionized particles? This is not new and is not related to the "big bang".
optical
Sep 19, 2016
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vidyunmaya
not rated yet Oct 27, 2016
visible-invisible matrix modes under shaded universe-may help in time- Space time Energy concepts
15 Books at LULU. http://www.lulu.c...jnani108

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