Why the earliest galaxies are causing drama and controversy among astronomers: shortwave

The James Webb Space Telescope is the most powerful telescope ever put into space. As such, it is helping to usher in a new era of astrophysics. Astronomers can now study galaxies older and at greater distances than ever before.

“If you were a paleontologist, you would dig deeper and deeper to find the oldest bones. In astronomy, what we do is look at our history,” he says. Jorge Moreno, associate professor of astronomy at Pomona College. “We have to look back in time, but we don’t have a time machine. So what we do is look at really far distances.”

As they look into the deep, distant history of the universe, scientists are surprised to discover that galaxies appeared in our cosmic history much earlier than scientists expected.

It’s a galactic controversy that has astronomers around the world excited and baffled.

So what is it about these galaxies that worries astronomers? JWST isn’t just finding galaxies in formation 200-500 million years after the Big Bang, but also that they are larger and brighter than astronomers expected.

Using light to look into the past

The most distant galaxies seen by the telescope are also some of the oldest galaxies in our universe. The James Webb Space Telescope can see them because it captures the faint light they emit.

When light from these reaches of the universe approaches the telescope, it is in the infrared light range and is no longer visible to the naked eye. Light visible to humans is only a fraction of the total range of light at the surface. electromagnetic spectrum.

This light has been traveling for a long time when it reaches the telescope. For reference, it takes about eight minutes for light to travel from the sun to the eye. The light from Proxima Centauri, the Sun’s closest stellar neighbor, takes just over four years to reach us here on Earth.

Seeing a teenager when you’re expecting a kindergartener

Light is a double-edged sword in the context of these galaxies. It is what allows us to study galaxies. But there is much more than astronomers would have expected.

The brightness of a galaxy can be related to its mass, because a galaxy’s light comes from stars. If one assumes a certain brightness and average mass of a star, one can roughly estimate the mass of a galaxy.

But many of the models that astronomers have done up to this point have led them to believe that there was not enough time for the galaxies to reach this mass in such a short time.

“It’s like if you went to a daycare and saw a teenager,” Moreno says.

However, Moreno says that this assumption that brightness equals mass may not always be accurate. For example, there could be an active supermassive black hole at the center of these first galaxies with bright accretion disks or high-energy jets that would make galaxies appear artificially massive. Or, if there is hot dust in the galaxies (which appears very bright in the infrared wavelengths captured by the James Webb Space Telescope), that would also make the galaxies appear more massive than they are.

When young galaxies are advanced for their age

Most galaxies fall into two types: spirals, which are disk-shaped with arms of dust and gas; and elliptical, which look more like spheres of soft light.

Until now, scientists thought that any galaxy from this relatively early period in the universe’s history would have been too young to have been forced into that binary yet. Instead, astronomers thought galaxies would be… masses. But Moreno and other astronomers like him are excited to now study what appear to be very structured galaxies.

“Some of them look very similar to galaxies in the local universe,” he says. “They appear to have additional structure and maybe even spiral arms. That wasn’t something we really expected.”

The high level of structure and brightness of these galaxies is leading some astrophysicists to question the age of the universe.

The universe does not appear to be more than 13.8 billion years old

Barely.

In an attempt to explain the strikingly bright, highly structured (and possibly quite massive) galaxies that exist so early in the universe’s timeline, some researchers have postulated that the universe is about twice as old as previously believed. They boost the age of the universe from a quick 13.8 billion years to about 26.7 billion years.

An article published earlier this year in the magazine Monthly notices from the Royal Astronomical Societyand He came to this conclusion after combining two models of the universe. One is the commonly accepted model for the expansion of the universe. This model explains that as the universe expands, light from galaxies must travel farther and therefore changes from a bluer to a redder light spectrum. The other model with which it is combined has been discredited. It’s called the tired light model and it claims that as light travels through the universe, it becomes redder because it “gets tired” or loses energy.

Moreno says that while he thinks combining the models is smart, it is not backed by scientific evidence.

“I think in science, if you already have a model that’s simpler than that, you should stick with it, unless you have extraordinary evidence to do otherwise.”

Moreno also warns people not to be too quick to accept this assumption that the universe is twice as old as previously thought. If true, scientists could prove it by directly observing stars and galaxies that are more than 13.8 billion years old, the currently accepted age of the universe.

No such evidence has been found.

Pausing to absorb ancient galactic wisdom

NASA receives more data from the James Webb Space Telescope every day, and with additional data comes possibilities for new solutions.

But for Moreno it is also important to pause for moments of reflection on the conclusions we draw from the observations.

So are the lessons of these galaxies, which according to Moreno alternately go through periods of brightness and dimming. “I think that’s something we need to learn from them: that it’s important to have moments when we’re really excited about discovering things. But there are times when we need to slow down, take a break, and really think about things clearly and slowly.”

This episode was produced by Rachel Carlson. It was edited by Rebecca Ramirez and Berly McCoy. Anil Oza verified the facts. Josh Newell was the audio engineer. Special thanks to James Davenport.

Questions or controversies? Email us at shortwave@npr.org.