Photo by: NASA, ESA, and T. Brown (STScI)

NASA, ESA, and T. Brown (STScI)

Small Galaxies Matter Too

Long ago, our universe was without stars. When that first generation ignited, it completely transformed the cosmos, ripping away the veil of neutral gas that had persisted for hundreds of millions of years. This process, called reionization, is largely mysterious to astronomers. But new research is revealing that the smallest of galaxies may have played the biggest of roles.

June 23, 2021

Long, long ago (and I mean long ago), our universe was much smaller, much hotter, and much denser. Over 13 billion years ago, our universe was a mere one thousandth of its present size and had an average temperature of thousands of degrees Kelvin.

This hot, dense soup was not a place to find galaxies or even stars. It was just one big never-ending plasma, which is the state of matter where electrons are ripped away from atomic nuclei.

But then the universe got bigger, got looser, got cooler. When our cosmos was about 380,000 years old, it cooled to the point where the electrons could settle into their atomic homes, rendering the gas in our universe neutral.

And dark. Very dark. Cosmologists call this epoch, which lasted for a few hundred million years, the “dark ages”, appropriately enough.

The subject of this NASA/ESA Hubble Space Telescope image is a dwarf galaxy named NGC 5949. Thanks to its proximity to Earth — it sits at a distance of around 44 million light-years from us, placing it within the Milky Way’s cosmic neighbourhood — NGC 5949 is a perfect target for astronomers to study dwarf galaxies. With a mass of about a hundredth that of the Milky Way, NGC 5949 is a relatively bulky example of a dwarf galaxy. Its classification as a dwarf is due to its relatively small number of constituent stars, but the galaxy’s loosely-bound spiral arms also place it in the category of barred spirals. This structure is just visible in this image, which shows the galaxy as a bright yet ill-defined pinwheel. Despite its small proportions, NGC 5949’s proximity has meant that its light can be picked up by fairly small telescopes, something that facilitated its discovery by the astronomer William Herschel in 1801.  Astronomers have run into several cosmological quandaries when it comes to dwarf galaxies like NGC 5949. For example, the distribution of dark matter within dwarfs is quite puzzling (the “cuspy halo” problem), and our simulations of the Universe predict that there should be many more dwarf galaxies than we see around us (the “missing satellites” problem).

The subject of this NASA/ESA Hubble Space Telescope image is a dwarf galaxy named NGC 5949. Thanks to its proximity to Earth — it sits at a distance of around 44 million light-years from us, placing it within the Milky Way’s cosmic neighbourhood — NGC 5949 is a perfect target for astronomers to study dwarf galaxies.

Photo by: ESA/Hubble & NASA

ESA/Hubble & NASA

The subject of this NASA/ESA Hubble Space Telescope image is a dwarf galaxy named NGC 5949. Thanks to its proximity to Earth — it sits at a distance of around 44 million light-years from us, placing it within the Milky Way’s cosmic neighbourhood — NGC 5949 is a perfect target for astronomers to study dwarf galaxies.

Eventually, matter began to coalesce to form the first stars and galaxies (the “cosmic dawn”). Through some as-yet-understood process, the radiation from those first stars blasted through the universe, ripping the neutral gas apart and returning it to its original plasma state – a state it has largely maintained in all the eons since.

Hubble's infrared vision pierced the dusty heart of our Milky Way galaxy to reveal more than half a million stars at its core. At the very hub of our galaxy, this star cluster surrounds the Milky Way's central supermassive black hole, which is about 4 million times the mass of our sun.

Photo by: NASA, ESA, and Hubble Heritage Team (STScI/AURA, Acknowledgment: T. Do, A.Ghez (UCLA), V. Bajaj (STScI)

NASA, ESA, and Hubble Heritage Team (STScI/AURA, Acknowledgment: T. Do, A.Ghez (UCLA), V. Bajaj (STScI)

Hubble's infrared vision pierced the dusty heart of our Milky Way galaxy to reveal more than half a million stars at its core. At the very hub of our galaxy, this star cluster surrounds the Milky Way's central supermassive black hole, which is about 4 million times the mass of our sun.

The biggest difficulty with trying to study this epoch in the history of our universe is that it’s incredibly far away from us, and our telescopes just aren’t yet good enough to directly witness this grand transformation. But new telescopes are on the case, and beginning to paint the initial sketches that will eventually (hopefully) become a full portrait.

And that initial sketch seems to involve a lot of small galaxies. New observations show that small, compact galaxies are capable of amazing feats of star formation, pumping out many more stars every year than galaxies like our own Milky Way.

This deep-field view of the sky, taken by NASA's Spitzer Space Telescope, is dominated by galaxies - including some very faint, very distant ones - circled in red. The bottom right inset shows one of those distant galaxies, made visible thanks to a long-duration observation by Spitzer.

Photo by: NASA/JPL-Caltech/ESA/Spitzer/P. Oesch/S. De Barros/ I.Labbe

NASA/JPL-Caltech/ESA/Spitzer/P. Oesch/S. De Barros/ I.Labbe

This deep-field view of the sky, taken by NASA's Spitzer Space Telescope, is dominated by galaxies - including some very faint, very distant ones - circled in red. The bottom right inset shows one of those distant galaxies, made visible thanks to a long-duration observation by Spitzer.

Among that star formation frenzy is a population of large, hot, radiation-blasting baddies. For the first time, astronomers caught those big stars from a small galaxy pumping out enough radiation to blast out the neutral gas surrounding it.

Dive Deeper into the Cosmos

Journey Through the Cosmos in an All-New Season of How the Universe Works

The new season premieres March 24 on Science Channel and streams on discovery+.

This kind of break-out could be beginning stages of the reionization of the universe that took place when it was only a few hundred million years old, shortly after the formation of the first stars and galaxies. Over time, it’s thought, expanding bubbles of radiation from small galaxies would go on to reionize all the gas in the universe.

Not too bad for a small galaxy.

Paul M. Sutter

Paul M. Sutter is an astrophysicist at Stony Brook University and the Flatiron Institute, host of Ask a Spaceman and Space Radio, and author of How to Die in Space.

Next Up

India’s Space Agency is Going Big… By Going Small

Astrophysicist Paul M. Sutter shares the latest in the world of rocket launches and what India’s SSLV is all about.

What We’ve Already Learned From James Webb? (Hint: it’s a lot)

That was worth the wait. Just a quick handful of months since its historic launch on Christmas Day, the James Webb Space Telescope has flown to its observing position, unfolded its delicate instruments and ultra-sized mirror, and run through a suite of checks and alignments and calibrations. The team at NASA behind the telescopes released their first batch of images from the science runs, and besides being gorgeous, they're powerful.

Why Astronomers Care About Super-Old Galaxies?

A long time ago, our universe was dark.It was just 380,000 years after the big bang. Up until that age, our entire observable cosmos was less than a millionth of its present size. All the material in the universe was compressed into that tiny volume, forcing it to heat up and become a plasma. But as the universe expanded and cooled, eventually the plasma changed into a neutral gas as the first atoms formed.

A Guide to this August’s Best Astronomy Attractions

Learn more about the exciting things happening in the night sky this month! From the rings of Saturn to the most popular meteor shower of the year, August 2022 has us stargazing all month.

How Astronomers Use a Trick of Gravity to See the Most Distant Objects in the Universe

Let’s say you’re an astronomer (work with me here) and you want to take a picture of something incredibly, deeply far away. You know, the typical business of astronomy.

South Korea Joins Space Race by Sending its First Spacecraft to the Moon

South Korea is launching its first lunar probe to the moon on August 4th. The Korea Pathfinder Lunar Orbiter (KPLO) or Danuri, developed by the Korea Aerospace Research Institute (KARI) is being launched to study moon carters, magnetic fields, and surface weathering.

How Exoplanets Became the Next Big Thing in Astronomy

To date, we know of over 5,000 planets outside the solar system. And astronomers suspect that there may be *checks notes* around a trillion more in our galaxy alone. The search for exoplanets is one of the hottest topics in astronomy, with expensive telescopes and giant collaborations all searching for the holy grail of the 21st century: an Earth 2.0, a habitable world like our own.

NASA and SpaceX are Going on a Date, and We're All Invited

Save the date--On May 27th, if everything goes as planned, a rocket will launch from Kennedy Space Center in Cape Canaveral, Florida. Watch SPACE LAUNCH LIVE: AMERICA RETURNS TO SPACE on Discovery and Science Channel starting at 2P ET.

Why Charting the Most Extreme Objects in the Solar System Matters

So the astronomers called it “FarFarOut”, which is mostly a joke because the last time they found such a distant object it they nicknamed it “FarOut”, and this new world is much, much, farther out.

6 Months in Space Permanently Ages Bones by 10 Years

Astronauts on long-term space missions can experience bone loss equivalent to two decades of aging. New research suggests more weight-bearing exercises in space could help offset that decline.

Related To: