Astronomers use observations of a gravitationally lensed galaxy to measure the properties of the early universe

October 26, 2016 by Sean Nealon, University of California - Riverside
The Cosmic Horseshoe, as photographed by the Hubble Space Telescope. Credit: ESA/Hubble & NASA.

Although the universe started out with a bang it quickly evolved to a relatively cool, dark place. After a few hundred thousand years the lights came back on and scientists are still trying to figure out why.

Astronomers know that reionization made the universe transparent by allowing light from distant to travel almost freely through the cosmos to reach us.

However, astronomers don't fully understand the escape rate of ionizing photons from early galaxies. That escape rate is a crucial, but still a poorly constrained value, meaning there are a wide range of upper and lower limits in the models developed by astronomers.

That limitation is in part due to the fact that astronomers have been limited to indirect methods of observation of ionizing photons, meaning they may only see a few pixels of the object and then make assumptions about unseen aspects. Direct detection, or directly observing an object such as a galaxy with a telescope, would provide a much better estimate of their escape rate.

In a just-published paper, a team of researchers, led by a University of California, Riverside graduate student, used a method and found the previously used constraints have been overestimated by five times.

"This finding opens questions on whether galaxies alone are responsible for the reionization of the universe or if faint dwarf galaxies beyond our current detection limits have higher escape fractions to explain radiation budget necessary for the reionization of the universe," said Kaveh Vasei, the graduate student who is the lead author of the study.

It is difficult to understand the properties of the early universe in large part because this was more than 12 billion year ago. It is known that around 380,000 years after the Big Bang, electrons and protons bound together to form hydrogen atoms for the first time. They make up more than 90 percent of the atoms in the universe, and can very efficiently absorb high energy photons and become ionized.

However, there were very few sources to ionize these atoms in the early universe. One billion years after the Big Bang, the material between the galaxies was reionized and became more transparent. The main energy source of the reionization is widely believed to be massive stars formed within early galaxies. These stars had a short lifespan and were usually born in the midst of dense gas clouds, which made it very hard for ionizing photons to escape their host galaxies.

Previous studies suggested that about 20 percent of these ionizing photons need to escape the dense gas environment of their host galaxies to significantly contribute to the reionization of the material between galaxies.

Unfortunately, a direct detection of these ionizing photons is very challenging and previous efforts have not been very successful. Therefore, the mechanisms leading to their escape are poorly understood.

This has led many astrophysicists to use indirect methods to estimate the fraction of ionizing photons that escape the galaxies. In one popular method, the gas is assumed to have a "picket fence" distribution, where the space within galaxies is assumed to be composed of either regions of very little gas, which are transparent to ionizing light, or regions of , which are opaque. Researchers can determine the fraction of each of these regions by studying the light (spectra) emerging from the galaxies.

In this new UC Riverside-led study, astronomers directly measured the fraction of ionizing photons escaping from the Cosmic Horseshoe, a that is gravitationally lensed. Gravitational lensing is the deformation and amplification of a background object by the curving of space and time due to the mass of a foreground galaxy. The details of the galaxy in the background are therefore magnified, allowing researchers to study its light and physical properties more clearly.

Based on the picket fence model, an escape fraction of 40 percent for ionizing photons from the Horseshoe was expected. Therefore, the Horseshoe represented an ideal opportunity to get for the first time a clear, resolved image of leaking ionizing photons to help understand the mechanisms by which they escape their .

The research team obtained a deep image of the Horseshoe with the Hubble Space Telescope in an ultraviolet filter, enabling them to directly detect escaping ionizing photons. Surprisingly, the image did not detect ionizing photons coming from the Horseshoe. This team constrained the fraction of escaping photons to be less than 8 percent, five times smaller than what had been inferred by indirect methods widely used by astronomers.

"The study concludes that the previously determined fraction of escaping ionizing radiation of galaxies, as estimated by the most popular indirect method, is likely overestimated in many galaxies," said Brian Siana, co-author of the research paper and an assistant professor at UC Riverside. "The team is now focusing on direct determination the fraction of escaping ionizing that do not rely on indirect estimates."

This paper, "The lyman continuum escape fraction of the cosmic horseshoe: a test of indirect estimates," has been published in the Astrophysical Journal.

Explore further: Explaining why the universe can be transparent

More information: Kaveh Vasei et al. THE LYMAN CONTINUUM ESCAPE FRACTION OF THE COSMIC HORSESHOE: A TEST OF INDIRECT ESTIMATES, The Astrophysical Journal (2016). DOI: 10.3847/0004-637X/831/1/38

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5 / 5 (4) Oct 26, 2016
To Who It May Concern,

This agrees with my theory that I sent to Kaptain Kangaroo and he posted it on his bulletin board in 1962, so I got that going for me.
2 / 5 (4) Oct 26, 2016
Hi Hat1208 (and IMP-9 et al if you are reading this). :)

The above also supports much of what I have been pointing out regarding the deep space local/intervening material/processes that attenuate all distant-sourced 'signal' EM radiations of all sorts, irrespective of universe theory (BB or Eternal etc).

And since these same factors DO seriously damage (ie falsify) many previous naive/simplistic assumptions/interpretations using CMB etc 'signals' (much of which were totally unjustifiably and unscientifically claimed as 'evidence' for BB/Expansion/inflation etc hypotheses which are now increasingly shown to have been objectively UN-tenable in both science and logics), isn't it about time we all got serious about rethinking it all properly and scientifically/logically, just as I have been trying to get everyone to do for themselves? :)
2.3 / 5 (3) Oct 27, 2016
Hi IMP-9, Phys1 et al. :)

I note you haven't commented on this.

Can you at least indicate whether you now have an inkling re the many problems/flaws which have caused decades of false assumptions/interpretations/claims to build up in the BB-related 'supporting evidence' catalogue?

Add this latest item to all the other recent years' worth of newer mainstream observations/reviews etc, and you may get the full picture of just how unscientifically the edifice for 'modern cosmology model' has been built up since BB/Inflation etc proponents departed from the objective logics/reality physics demands of true scientific methodology.

Phys1, putting me on ignore says you are biased against anything that may unsettle your denialist state; which makes you just as unscientific as the religious/ignoramus trolls you attack; actually, worse; because you should know/be better.

Good luck catching up with the newer mainstream works increasingly confirming me correct on many fronts, guys! :)
Oct 27, 2016
This comment has been removed by a moderator.
2.3 / 5 (3) Oct 27, 2016
Hi Hat1208. :)

Holy frickin moly!
Too right, mate. It's come to a terrible pass when the one called 'crank' etc turns out to have been correct all along while the detractors have been found to be incorrect all along, hey? :)

So, did you have anything to say on the flaws/problems I have been pointing out to IMP-9 for ages now, and which the above article confirms me correct about all along? Or are you here to take cheap shots at religious/ignoramus/trolls instead of getting yourself up to date with all that I have been pointing out to IMP-9? Ask him, he'll tell you all about it (I am trusting him to not be in denial anymore). Good luck, Hat1208. :)
1 / 5 (2) Oct 27, 2016
Oops, double post removed.
1 / 5 (2) Oct 27, 2016
sub: evolve Creative Function
Forget about Big-bang -Self contradictions even from Galactic Plane.
gravitational mode limits development of the subject.
creative- Cosmic Function of the Universe-promote orderliness not chaos.

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