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Thursday, June 24, 2021

Explained: How are the number of stars in the Universe counted?

In order to roughly estimate the number of stars in the Universe, scientists have estimated that on average each galaxy consists of about 100 million stars, but this figure is not exact.

By: Explained Desk | New Delhi |
Updated: June 8, 2021 10:03:39 am
nasa rocket launch to count stars in universeWhile this is not the first time that such a mission has been undertaken, the CIBER-2 instrument has been improved upon to see if any stars had been undercounted in the previous counting attempts. (Twitter/@NASA)

On June 6, a NASA-funded rocket’s launch window will open at the White Sands Missile Range in New Mexico, USA. The aim of this mission is to count the number of stars that exist in the Universe.

While this is not the first time that such a mission has been undertaken, the CIBER-2 instrument has been improved upon to see if any stars had been undercounted in the previous counting attempts.

So what is CIBER-2?

In order to roughly estimate the number of stars in the Universe, scientists have estimated that on average each galaxy consists of about 100 million stars, but this figure is not exact. The figure of 100 million could easily be an underestimation, probably by a factor of 10 or more.

To put this into perspective, an average of 100 million stars in each galaxy (there an estimated 2 trillion of them as per NASA), would give a total figure of one hundred quintillion stars or 1 with 21 zeroes after it. NASA notes that if this figure is accurate it would mean that for every grain of sand on Earth, there are more than ten stars.

But this calculation assumes that all stars are inside galaxies, which might not be true and this is what the CIBER-2 instrument will try to find out.

This instrument will launch aboard a sounding rocket, a small suborbital rocket that will carry scientific instruments on brief trips into space before it falls back to Earth for recovery.

The European Space Agency (ESA) says there could be 100 thousand million stars in the Milky Way alone. So if there are 1011 to 1012 stars in the galaxy and around the same number of galaxies, it would mean a total of 1022 to 1024 stars in the Universe.

How will CIBER-2 count stars?

Once the instrument is above Earth’s atmosphere, it will survey a patch of sky that will include dozens of clusters of galaxies. Even so, NASA notes that the instrument will not actually count individual stars but it will instead detect the extragalactic background light, which is all of the light that has been emitted throughout the history of the Universe.

From all of this extragalactic background light, the CIBER-2 will focus on a portion of this called cosmic infrared background, which is emitted by some of the most common stars. Essentially, this approach is aiming to look at how bright this light is to give scientists an estimate of how many of these stars are out there.

The ESA infrared space observatory Herschel also counted the number of galaxies in infrared and measured their luminosity previously.

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