Travel the universe with Dr. Ethan Siegel as he answers the biggest questions of all
The current record-holder is a doozy, and right at the limit of what Hubble can do. But there’s even more out there.
The greatest advances in science often come when we first probe new frontiers.
Our entire cosmic history is theoretically well-understood, but only qualitatively. It’s by observationally confirming and revealing various stages in our Universe’s past that must have occurred, like when the first stars and galaxies formed, that we can truly come to understand our cosmos. (Nicole Rager Fuller / National Science Foundation)
When we peered into the abyss of space more deeply than ever, we revealed thousands of distant galaxies.
Various long-exposure campaigns, like the Hubble eXtreme Deep Field (XDF) shown here, have revealed thousands of galaxies in a volume of the Universe that represents a fraction of a millionth of the sky. All told, we estimate there are two trillion galaxies contained within the observable Universe. (NASA, ESA, H. Teplitz and M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (Arizona State University), and Z. Levay (STScI))
To view them, three obstacles must be overcome: their faintness, their apparent redness, and the intervening neutral matter.
Light may be emitted at a particular wavelength, but the expansion of the Universe will stretch it as it travels. Light emitted in the ultraviolet will be shifted all the way into the infrared when considering a galaxy whose light arrives from 13.4 billion years ago.(Larry McNish of RASC Calgary Center)
The most distant galaxies appear very red, because their emitted light’s wavelength gets stretched by expanding space.
As the fabric of the Universe expands, the wavelengths of distant light sources get stretched as well. In the case of the first stars, this can turn far-UV light all the way into mid-IR light. (E. Siegel / Beyond The Galaxy)
We overcome this by looking at longer, infrared wavelengths of light.
Although there are magnified, ultra-distant, very red and even infrared galaxies in the eXtreme Deep Field, there are galaxies that are even more distant out there. (NASA, ESA, R. Bouwens and G. Illingworth (UC, Santa Cruz))
The great distances leave them faint, so we must rely on Einstein’s natural magnifying glass to expose them.
A large foreground mass, like a massive galaxy or galaxy cluster, can stretch, distort, but more importantly magnify the light from a background galaxy if the configuration is ideal. (NASA/ESA/A. Gonzalez (U. of Florida), A. Stanford (UC Davis), and M. Brodwin (U. of Missouri))
Foreground galaxies, and large galaxy clusters, act as a gravitational lens, revealing these most distant galaxies.
The galaxy cluster MACS 0416 from the Hubble Frontier Fields, with the mass shown in cyan and the magnification from lensing shown in magenta. That magenta-colored area is where the lensing magnification will be maximized. Mapping out the cluster mass allows us to identify which locations should be probed for the greatest magnifications and ultra-distant candidates of all.(STScI/NASA/CATS Team/R. Livermore (UT Austin))
Finally, beyond a certain distance, the Universe hasn’t formed enough stars to reionize space and make it 100% transparent.
Schematic diagram of the Universe’s history, highlighting reionization. Before stars or galaxies formed, the Universe was full of light-blocking, neutral atoms. While most of the Universe doesn’t become reionized until 550 million years afterwards, a few fortunate regions are mostly reionized at much earlier times. (S. G. Djorgovski et al., Caltech Digital Media Center)
We only perceive galaxies in a few serendipitous directions, where copious star-formation occurred.
Only because this distant galaxy, GN-z11, is located in a region where the intergalactic medium is mostly reionized, can Hubble reveal it to us at the present time. To see further, we require a better observatory, optimized for these kinds of detection, than Hubble.(NASA, ESA, and A. Feild (STScI))
The enormous ‘dip’ that you see in the graph here, a direct result of the latest study from Bowman et al. (2018), shows the unmistakable signal of 21-cm emission from when the Universe was between 180 and 260 million years in age. This corresponds, we believe, to the turn-on of the first wave of stars and galaxies in the Universe. Based on this evidence, the turn-on begins at a redshift of 22 or so. (J.D. Bowman et al., Nature, 555, L67 (2018))
At greater distances and corresponding to earlier times, the light from ever-distant galaxies will appear to be redshifted more severely. Hubble can go out to about 1.6 microns in wavelength, but that is not enough to get the first galaxies that ought to exist. (E. Siegel)
We must go farther into the infrared than Hubble’s capabilities allow.
The James Webb Space Telescope vs. Hubble in size (main) and vs. an array of other telescopes (inset) in terms of wavelength and sensitivity. It should be able to see the truly first galaxies, even the ones that no other observatory can see. Its power is truly unprecedented. (NASA / JWST science team)
That requires the James Webb Space Telescope.
The first stars and galaxies in the Universe will be surrounded by neutral atoms of (mostly) hydrogen gas, which absorbs the starlight. The hydrogen makes the Universe opaque to visible, ultraviolet, and a large fraction of infrared light. We must go to long wavelengths to have a chance. (Nicole Rager Fuller / National Science Foundation)
Mostly Mute Monday tells the astronomical story of an object, region, or phenomenon in the Universe in images, visuals, and no more than 200 words. Talk less, smile more.
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