How many galaxies are there in our observable universe?

Our universe contains a vast number of galaxies and very few of them have been detected by astronomers. We already know about our home galaxy Milky Way and the neighboring Andromeda galaxy but how many galaxies are there exactly, apart from what we know?

The Hubble Space Telescope has been enriching us with unknown images of space. NASA’s Hubble Space Telescope creates an image of space after combining several images for 10 years of observation called a Hubble eXtreme Deep Field (XDF) vision. According to astronomers if you cover the moon with your thumb then the XDF area would be about the size of a head of a pin. The XDF has successfully revealed thousands of both near and distant galaxies after careful observation. NASA’s Hubble has currently detected a sizable amount of galaxies between 100-200 billion says the Space Telescope Science Institute’s astrophysicist Mario Livio.

Livio said that since the Hubble telescope launched in 1990, it went through a vast amount of upgrades since then. In 1995 astronomers detected approximately 3000 faint galaxies in a single frame in the apparently empty region of Ursa Major via Hubble telescope. According to Weber State University, this image represented the most furthest any telescope would ever go at that time.

NASA says that in 2003-04 Hubble went through an upgrade and created the Hubble Ultra Deep Field images. With this technological improvement Hubble observed almost 10,000 galaxies within just million-second exposure in a small spot in the constellation Fornax.

In 2012 with more degradation Hubble detected approximately 5,500 galaxies within a narrow field view. Astronomers say that Hubble has so far estimated almost 100 billion galaxies in our universe.

According to astronomers, every portion of space involves the same method for estimating the number of galaxies. So, they stated that the universe is homogeneous. Livio said, “This is assuming that there is no large cosmic variance, that the universe is homogenous. We have good reasons to suspect that is the case. That is the cosmological principle.”

NASA also stated, “The simplest assumption to make is that if you view the contents of the universe with sufficiently poor vision, it would appear roughly the same everywhere and in every direction. That is, the matter in the universe is homogeneous and isotropic when averaged over very large scales. This is called the cosmological principle.”

Recently, NASA’s James Webb Space Telescope also successfully captured images of space. It released its deep-field image on July 12, 2022. NASA’s Webb telescope is responsible for capturing distant galaxies formed following the Big Bang 13.8 billion years ago. The Webb’s telescope captured the massive galaxy cluster Abell 2744 with the ability to distort the space around it. The Webb images are being studied in a program called the Grism Lens-Amplified Survey from Space or GLASS. Astronomers are currently scrutinizing galaxy candidates GLASS-z11 and GLASS-z13 with a redshift of 11 and 13 respectively. Redshift is the measurement of how the light emitted from a galaxy can be stretched by the expansion of the universe. The higher the redshift the furthest will be the source. The galaxies 11 and 13 existed over 13.4 billion years ago means just 400-300 million years after the Big Bang. Webb’s Near Infrared Spectrograph has been used to measure the redshifts of these galaxies. Webb’s images also stated that these early galaxies were more luminous and fast forming. Both of these traits can be used to locate the regions of galaxy formation in the primitive universe. Scientists have said that these galaxies are formed from concentrated matter which can explain the distribution of normal and dark matter right after the Big Bang.

According to astronomers the universe we can see is the observable universe and the universe is expanding faster than the speed of light. Astrophysicist Livio said, “We can only see light from galaxies whose light had enough time to reach us. It doesn’t mean that that’s all there is in the universe. Hence, the definition of the observable universe.”

Astronomers anticipate that as Hubble could detect galaxies formed 450 million years after the Big Bang, the James Webb Space Telescope could be able to spot galaxies formed almost 200 million years after the Big Bang. At the same time, Livo said that the observable universe contains 200 billion galaxies, however, with the help of Webb’s telescope the number is not going to change rather we would be able to find more in our lifetime within the limits of our observable universe.

Livio said, “The numbers are not going to change much. So a number like 200 billion (galaxies) is probably it for our observable universe.”




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