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Starts With A Bang

How lucky was Hubble to find the most distant galaxy ever?

From 13.4 billion years ago, the current record-holder is unlikely to fall anytime soon. Why? A combination of science… and luck.

“We’ve taken a major step back in time, beyond what we’d ever expected to be able to do with Hubble. We see GN-z11 at a time when the universe was only three percent of its current age.” –Pascal Oesch

If you take the world’s most powerful space telescope, point it into the cosmic abyss for days, and collect all the light possible, you’ll see something fantastic.

The full UV-visible-IR composite of the Hubble eXtreme Deep Field; the greatest image ever released of the distant Universe. Image credit: NASA, ESA, H. Teplitz and M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (Arizona State University), and Z. Levay (STScI).

But you won’t see the Universe’s most distant galaxy.

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. Image credit: NASA, ESA, R. Bouwens and G. Illingworth (UC, Santa Cruz).

The most distant galaxy ever discovered comes from when the Universe was only 400-million-years-old, 3% of its current age.

It took four separate circumstances coming together all at once to make its discovery possible.

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. Image credit: Larry McNish of RASC Calgary Center.

1) The Universe is expanding, meaning that the wavelength of the emitted light gets stretched as it journeys throughout the Universe. We had to look in the infrared for light that was emitted in the ultraviolet, at more than double the wavelength limit of visible light.

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 earlier times. Image credit: S. G. Djorgovski et al., Caltech Digital Media Center.

2) The galaxy happens to be located where there’s no intervening neutral gas, since that would block the light we could see.

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. Image credit: NASA, ESA, and A. Feild (STScI).

A reionized region this early is rare, and purely serendipitous.

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. Image credit: NASA/ESA/University of Florida, Gainsville/University of Missouri-Kansas City/UC Davis.

3) We had to look near a very large mass, so that the Einsteinian effect of gravitational lensing could magnify the background galaxy. And…

Objects located a great distance away have their spectral lines redshifted. The presence of ionized hydrogen and oxygen lines at these great distances enable us to pinpoint exactly how far away a galaxy like GN-z11 is. Image credit: Ed Janssen, ESO.

4) We needed spectroscopic confirmation, to know this wasn’t simply an intrinsically red/infrared object.

The Great Observatories Origins Deep Studies North field (GOODS-N), cropped to show the Universe’s most distant galaxy, in red. All four of these circumstances needed to come together at once to make this galaxy’s discovery possible. Image credit: NASA, ESA, G. Illingworth (University of California, Santa Cruz), P. Oesch (University of California, Santa Cruz; Yale University), R. Bouwens and I. Labbé (Leiden University), and the Science Team.

Hubble’s record-holder, GN-z11, will likely stand until James Webb comes online.

James Webb will have seven times the light-gathering power of Hubble, but will be able to see much farther into the infrared portion of the spectrum, revealing those galaxies existing even earlier than what Hubble could ever see. Image credit: NASA / JWST science team.

We’ve gotten very lucky.

Mostly Mute Monday tells the astronomical story of an object, phenomenon or discovery in visuals, pictures and no more than 200 words.

Ethan Siegel is the author of Beyond the Galaxy and Treknology. You can pre-order his third book, currently in development: the Encyclopaedia Cosmologica.


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