Bad astronomy | Gravitational lens “molten ring” galaxy produces stars



A galaxy a billion light-years from Earth is pouring out copious amounts of infrared light, the hallmark of a furious starbirth.

It’s already pretty cool, but it’s better: As light from this galaxy passes through the Universe, it passes through a massive cluster of galaxies that warp it, amplifying its brightness, repeatedly cloning and twisting it into what looks like a river of molten gold.

I want to say, seriously. Check it out.


This gorgeous twisted weirdness is called WISE J022057.56-383311.4 – it was first seen in pictures by the wide-field infrared survey satellite, and the numbers are its coordinates in the sky; let’s call it J0220 for short – and it was chosen for study because astronomers are interested in a population of galaxies called Submillimeter (bright) galaxies, or SMG. These galaxies are bright at wavelengths between infrared and radio (submillimeter light has a wavelength of less than a millimeter) because they make many, many stars. When stars die, they generate dust, grains of carbon and silica which, when warmed by other stars, glow at submillimeter wavelengths (if this sounds familiar to you, it may be – be because we know that dying stars like Betelgeuse produce a lot of dust and that’s probably why the star has faded so much recently).

These galaxies were most common when the Universe was around 2-4 billion years old. The Universe is now 13.8 billion years old, so it took around 10 to 12 billion years for light from these galaxies to get here. In other words, we see them almost clearly across the observable Universe.

J0220 had characteristics that resembled an SMG, so astronomers who studied it followed with the APEX telescope to confirm this, and used previously observed archived data to measure the distance to this galaxy of over 9 billion light years. The Hubble images were taken by another astronomer in 2015, and used to aid in analysis.

The image is not a natural color; what is displayed in blue uses a green filter, green is a combination of green and red, and what you see in red is from an infrared filter. The combination produces this beautiful golden hue.

So that’s the color. And this shape?

Coincidentally, there is a massive cluster of galaxies called GAL-CLUS-022058 about 4 billion light-years away for us, and it’s located almost exactly between us and J0220. The cluster is huge, with hundreds of galaxies totaling one mass 100,000 billion times that of the Sun. That’s a lot of gravity, which quite severely distorts the space-time around the cluster. Light from the most distant galaxy passed through this chain, twisted into an arc, multiplied into four distinct images, and brightened on average by a factor of 18. This effect is called gravitational lens, and you can read all about how it works in a previous article.

It is really useful! Because it is illuminated by the lens, it is easier to study the galaxy despite the distortion. Even with this, you can see that it is a spiral galaxy and has blue arms indicating active star formation (massive stars are bluer and brighter, so these short-lived stars dominate the colors. visible light when a galaxy has a lot of stars).

By combining all the observations, astronomers find that J0220 emits infrared light from all the hot dust it contains up to a trillion times the energy of the sun. The galaxy itself probably only contains half the number of stars in our Milky Way galaxy, but there is so much dust converting this light to infrared that it glows fiercely at these wavelengths.

Using this number to calculate the rate of star formation indicates that J0220 produces stars at about 70 to 170 times the mass of the Sun per year. It’s a lot; the Milky Way produces only about 2 – yes, twice – the mass of stars in the Sun per year. I note that the rate is an average. It’s not like 70 to 170 new stars come out of J0220 every year! First, stars take a long time to form, so there is not a moment when a is born. Also, the rate is given in terms of mass, but most stars have a mass less than that of the Sun (red dwarfs, the most common stars, have 0.1 to 0.5 times the mass of the Sun, more or less). The math gets a bit complicated, but in reality a solar mass means that maybe 10 stars are actually formed. So 70 to 170 solar masses per year translates to, say, 700 to 1,700 million stars per million years.

Whichever way you look at it, it’s a lot of stars! 50 times or more the rate at which they are born in our own galaxy. J0220 becomes busy.

The formation of stars in the Universe is not a constant. It took a few billion years for galaxies to organize and really start to trigger them; the period of about 2 to 4 billion years after the Big Bang is called “cosmic noon” because that is when star formation peaked. In general, cosmically, it has been declining ever since.

The stars born then are like the baby boomers now; aging but still dominating things, so they are a key demographic in the stellar population and we need to understand them to understand how galaxies behave. And that means looking at galaxies three-quarters of the observable Universe to see what was happening when those stars were born. J0220 appears to be one of the brightest in its class, made even brighter for us by a physics quirk and positional coincidence.

Sometimes luck plays a role in science and in this case also produces exceptional beauty, a natural work of art with the colors of a Klimt and the shape of a Dali. Together, science and art paint a portrait of the young cosmos.


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