How do scientists search for stars and galaxies millions of light years away?



How do scientists search for stars and galaxies millions of light years away?

In: Technology

You must have heard of the HUBBLE Space Telescope. Launched in 1990, orbiting Earth at around 560 km altitude, with it’s 2.4 meter objective, it’s four main instruments can observe in the near Ultraviolet, visible and near infrared spectra. Hubble can see the dimmest and faintest objects out there of any telescope we’ve ever built, and can do so to wavelengths entering the near infrared. In theory, it could pick up traces of once-ultraviolet light from objects from when the Universe was just 400 million years old.

But Hubble can not verify precisely just how far the observed galaxies are. For this purpose, astronomers need to measure the precise wavelengths that the emission and absorption features from a galaxy are, and for this, they use ground-based spectroscopy. And that in turn means that they turn to the largest telescopes ever built, such as the 10-meter Keck telescopes in Hawaii, which houses the newly-installed MOSFIRE spectrometer, perfected for infrared observations.

Talking about distances, the latest find – galaxy EGS8p7, observed and measured by Hubble just a few months ago, was confirmed to have a red shift of 8.63 – the highest redshift of any galaxy ever, meaning that its emission lines are a factor of 863% longer in wavelength today than when they were emitted. The light from this object comes from when the Universe was just 588 million years old, or just 4% of its age.

[When galaxies are moving away from us at high speeds, it causes the light to redshift, by stretching its wavelength. The energy of a photon is defined by its wavelength, so if the wavelength is stretched due to the doppler effect, it drops to a lower energy and hence becomes red in color. For a galaxy whose light was emitted more than 13 billion years ago, that redshift is so severe that the ultraviolet light emitted by its atoms gets shifted all the way past the visible light portion and into the infrared. Shift that light some more, and even the Hubble Space Telescope won’t be able to detect it.]

All records are meant to be broken. The above record won’t stand for long! Another newer, bigger telescope is being built. Known as the James Webb Space Telescope due to be launched in 2018. This has a 6.50 meter objective offering un-precedented resolution and sensitivity.

it should not only dwarf the light-gathering power of Hubble, it is designed to probe farther infrared wavelengths than Hubble has ever dreamt of. Unlike Hubble, which can reach wavelengths of about 1.5 microns, James Webb can go all the way out past ten microns, meaning it can see all the way back to the first galaxies and potentially beyond, even all the way back to the first stars.