{"id":28757,"date":"2022-01-20T13:30:50","date_gmt":"2022-01-20T13:30:50","guid":{"rendered":"https:\/\/www.skyatnightmagazine.com\/?p=103777"},"modified":"2022-01-20T13:45:12","modified_gmt":"2022-01-20T13:45:12","slug":"why-do-astronomers-observe-the-universe-in-infrared","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/rss_feed\/why-do-astronomers-observe-the-universe-in-infrared\/","title":{"rendered":"Why do astronomers observe the Universe in infrared?"},"content":{"rendered":"

<\/p>

By Professor Michael Rowan-Robinson\n \t\t<\/p>

Published: Thursday, 20 January 2022 at 12:00 am<\/p>

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Infrared is a form of electromagnetic radiation exactly like visible light, but with a longer wavelength.<\/p>\n

The infrared waveband extends from 0.8 to 1,000 microns.<\/p>\n

In astronomy, infrared enables us to view elements of the Universe that are invisible to the human eye.<\/p>\n

\""Hidden\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
Hidden stars of the Eta Carinae Nebula are revealed in infrared red light in this image captured by the Very Large telescope. Credit: ESO\/T. Preibisch<\/span><\/figcaption><\/div>\n

Most of the infrared radiation from the night sky is absorbed by molecules of water and carbon dioxide in the Earth\u2019s atmosphere, though there are a few atmospheric \u2018windows\u2019, which allow observations by telescopes on the ground.<\/p>\n

It is only from space that we can see the full splendour of the infrared sky.<\/p>\n

Infrared was first discovered by astronomer William Herschel<\/a> in 1800, when he split sunlight using a prism and measured the temperature beyond the red end of the spectrum.<\/p>\n

\""An\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
Infrared light reveals heat emanating from different sources. Credit: Cultura RF\/Joseph Giacomin\/Getty Images<\/span><\/figcaption><\/div>\n

We experience infrared when we feel the radiant heat from a fire or from human bodies, which we cannot see.<\/p>\n

In astronomy, the importance of infrared wavelengths is their capacity to draw back the veil of obscuring dust that hides so much of the starlight of the Universe.<\/p>\n

As much as two thirds of all light emitted by stars is absorbed by interstellar dust and re-emitted at infrared wavelengths.<\/p>\n

Why is infrared astronomy used to study star formation?<\/strong><\/h2>\n
\""A\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
A radio and infrared image of a section of the Milky Way. Radiation from newborn stars heats cosmic dust that glows in infrared (in violet). Ultraviolet light from these stars gives off radio waves in red. Credit: NRAO\/AUI\/NSF<\/span><\/figcaption><\/div>\n

Only in the infrared part of the spectrum can we really assess how much star formation<\/a> is actually taking place in galaxies<\/a>, and how this changes with time.<\/p>\n

Regions in our own Milky Way Galaxy and others where new stars form are completely shrouded by dust, making infrared surveys crucial in trying to understand not just the origins of stars but of planetary systems too.<\/p>\n

These small, sub-micron-sized dust grains are where most of the elements made in stars are stored.<\/p>\n

\""Coalsack\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
The Coalsack Nebula is visible to the naked eye in the southern skies and is an example of the obscuring effect of an interstellar dust cloud. Credit: David Slack<\/span><\/figcaption><\/div>\n

The atoms of our bodies: carbon, nitrogen, oxygen and so on, were once locked up in dust grains between the stars.<\/p>\n

Infrared observations help us to understand the composition of these grains and hence the chemical evolution of interstellar material.<\/p>\n

They also help us to find out the physical conditions, density and temperature of the gas in regions where stars are forming.<\/p>\n

In our Galaxy, the fraction of starlight absorbed by dust is about 30%, but when galaxies are younger this fraction is much higher.<\/p>\n

Newly-formed stars are, in fact, totally shrouded by dust. So we can only trace out the history of star formation in the Universe by surveying in the infrared.<\/p>\n

Using infrared to search for exoplanets<\/b><\/h2>\n
\""A\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
A near-infrared image of exoplanet 51 Eridani b captured by the Gemini Planet Imager on 18 December 2014. Credit: J. Rameau (UdeM) and C. Marois (NRC Herzberg).<\/span><\/figcaption><\/div>\n

The infrared is also the ideal wavelength band to search for direct evidence of giant exoplanets<\/a> and brown dwarfs \u2013 objects that are not quite massive enough to ignite nuclear burning and turn into stars.<\/p>\n

The Infrared Astronomical telescope, IRAS, found several examples of stars surrounded by debris discs that are believed to be potential planetary systems in the making.<\/p>\n

On the larger scale, the Japanese Akari mission searched for infrared monsters \u2013 galaxies hundreds of times more luminous than our Milky Way<\/a>, which emit 99% of their output as infrared radiation.<\/p>\n

\""An\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
An all-sky view in infrared captured by the AKARI space telescope. The Milky Way is the bright band stretching across the image. Credit: JAXA<\/span><\/figcaption><\/div>\n

Large-scale surveys can detect star-forming galaxies back to the first billion years of the Universe.<\/p>\n

A second factor that drives us towards the infrared is the cosmological redshift.<\/p>\n

The infrared Spitzer Space Telescope<\/a> found galaxies with redshifts greater than six, which emit no optical light at all. Their redshifted starlight is detectable only in the infrared.<\/p>\n

It is for this reason that the successor to the Hubble Space Telescope<\/a>, the James Webb Space Telescope<\/a> (JWST), is primarily an infrared instrument.<\/p>\n

For more on this, read our guide on how JWST will observe exoplanets<\/a> and how JWST will observe galaxies<\/a>.<\/p>\n

\""Composite\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
Composite infrared images of Cassini\u2019s moon Enceladus, revealing geologic activity. Credit: NASA\/JPL-Caltech\/University of Arizona\/LPG\/CNRS\/University of Nantes\/Space Science Institute<\/span><\/figcaption><\/div>\n

A history of infrared observations<\/b><\/h2>\n

The James Webb Space Telescope is the latest in a long line of infrared space telescopes.<\/p>\n

The first, IRAS, surveyed the whole sky at wavelengths of 12 to 100 microns in 1983.<\/span><\/p>\n

IRAS made discoveries in many <\/span>different areas of astrophysics:<\/p>\n