George's Random Astronomical Object

Object 73: IRAS 10214+4724

Podcast release date: 16 May 2022

Right ascension: 10:24:34.5

Declination: +47:09:11

Epoch: J2000

Constellation: Ursa Major

Corresponding Earth location: An area near the Kuril-Kamchatka Trench in the Pacific Ocean

IRAS 10214+4724 is yet another one of these objects with a name that includes the object's coordinates, and in this situation, the coordinates are from an older out-of-use coordinate system. The word IRAS is the name of the telescope that found the object; the letters stand for the Infrared Astronomical Satellite. I'm just going to call this IRAS 10214 for short for the rest of this episode.

IRAS was a telescope launched into space in 1983 that made observations of the entire sky at far-infrared wavelengths [1]. This telescope was groundbreaking because the infrared astronomical observations that had been performed previously had been of just a very few very specific locations in the sky. IRAS's observations led astronomers to discover that relatively ordinary looking stars and galaxies were actually really strong infrared sources, and the telescope's all-sky maps also found new infrared-bright objects that had not previously been seen at visible wavelengths. However, the telescope made images that were blurrier than what the human eye can see in the visible part of the electromagnetic spectrum, so a lot of things like smaller nebulae, disks of dust orbiting other stars, and most galaxies looked like infrared smudges. Nonetheless, astronomers learned a lot from this telescope.

Astronomers working with the IRAS satellite discovered that a lot of galaxies produced a lot of infrared radiation, including the galaxy IRAS 10214. Some of these objects were nearby galalxies that were producing relatively normal amounts of infrared light but that looked bright in the infrared just because they were close. Other objects were more distant galaxies that were producing much more infrared radiation, so even though they were located relatively far away, they still looked similar in infrared brightness to nearby galaxies as seen from Earth. You can think of this as similar to comparing an ordinary light bulb located at arm's length to a set of stadium lights located much further away. Both could look the same brightness, but the stadium lights are clearly producing more photons.

Infrared radiation in space mainly comes from interstellar dust that absorbs ultraviolet and visible light and re-radiates that energy as infrared light. While interstellar dust is found throughout both our galaxy and other galaxies, it tends to be denser in the nebulae where stars are forming. These regions also contain lots of hot blue stars that produce huge amounts of ultraviolet and visible light that heat up the interstellar dust, which makes the locations where stars are forming very bright at infrared wavelengths.

Given this, we can say that nearby galaxies that are producing normal levels of infrared radiation are forming stars at a relatively normal rate while the more distant galaxies that produce larger amounts of infrared radiation are forming abnormally large numbers of stars. Additionally, many of these infrared-bright galaxies contain active galactic nuclei (AGN). AN AGN contains a supermassive black hole millions or billions of times the mass of the Sun that is surrounded by a disk of infalling gas. As that material falls into the black hole, it gets gravitationally compressed and really hot, and it produces a broad range of electromagnetic radiation. A lot of this radiation gets absorbed by interstellar dust near the AGN; the standard models typically depict the dust as lying within a thick ring around the disk of hot, infalling gas. The energy absorbed by the dust is re-radiated as infrared radiation, and it looks like such AGN may be responsible for producing large fractions of the infrared light emitted by many infrared-bright distant galaxies.

These infrared-bright galaxies that either are forming extreme numbers of stars or contain these AGN are commonly referred to as luminous or ultraluminous infrared galaxies [2]. Ever since their discovery by the IRAS satellite, they have attracted a lot of attention from astronomers. However, the most extreme of the objects discovered by the IRAS satellite was the galaxy IRAS 10214. This was the most distant object seen by the IRAS satellite, which also means that it has the interesting distinction of being the most distant infrared source that anyone knew about in the 1980s [3, 4]. Astronomers have determined that the light travelled about 10.8 billion years from the galaxy IRAS 10214 to reach the Earth [3]. For the IRAS satellite to have been able to see this galaxy, it had to be producing several times more infrared radiation than a typical ultraluminous infrared galaxy [3]. It actually turned out to be in a new category of galaxies, so it was called a hyperluminous infrared galaxy. Imagine an already abnormal ultraluminous infrared galaxy that contains both a supermassive black hole and that is forming lots of stars. Now imagine that that galaxy consumed a six pack of galaxy-sized energy drinks, and that is an apt description of IRAS 10214.

One of the main reasons why IRAS 10214 can be so easily seen from so far away is because its light is being gravtiationally lensed. Using Hubble Space Telescope observations from 1994, Peter Eisenhardt and his collaborators demonstrated that another galaxy sits between Earth and IRAS 10214, and the gravitational forces from this closer galaxy have bent or lensed the light, including the infrared light, from IRAS 10214 towards the Earth, thus making IRAS 10214 look abnormally bright [4]. The light from IRAS 10214 also looks rather distorted in these Hubble Space Telescope images. The nearby galaxy that is bending the light from IRAS 10214 looks like a roughly circular object, while the light from IRAS 10214 itself appears in two different places on either side of the closer galaxy. On one side, the light from IRAS 10214 looks like a dot, while on the other side, it looks like an arc. You could imagine IRAS 10214 looking like a smiling cyclops, with the nearby galaxy forming the nose of the cyclops.

While IRAS 10214 was a rather special discovery in the 1980s, astronomers have since discovered many more very distant infrared-bright galaxies whose light has been gravitationally lensed by nearby galaxies. (I myself am even writing a science paper on these types of galaxies right now. Well, not while I'm recording, but you know what I mean.) These objects are great for a number of reasons, but I will highlight two of the major reasons why astronomers like looking at these objects. First, the gravitational lensing, while distorting the appearance of the more distant galaxies, allows astronomers to actually detect objects that they would otherwise normally not be able to see [5, 6, 7]. Second, astronomers can use models of the lensing to determine how matter is distributed within the closer galaxies, and this is an excellent way to search for dark matter [8]. Gravitational lenses also just plainly look cool. So, the next time to hear about astronomers discussing why they are so excited to see a gravitationally lensed galaxy, you hopefully understand how exciting these things are.

References

[1] Neugebauer, G. et al., The Infrared Astronomical Satellite (IRAS) mission., 1984, Astrophysical Journal Letters, 278, L1

[2] Sanders, D. B. and Mirabel, I. F., Luminous Infrared Galaxies, 1996, Annual Reviews of Astronomy and Astrophysics, 34, 749

[3] Rowan-Robinson, M. et al., A high-redshift IRAS galaxy with huge luminosity-hidden quasar or protogalaxy?, 1991, Nature, 351, 719

[4] Eisenhardt, Peter R. et al., Hubble Space Telescope Observations of the Luminous IRAS Source FSC 10214+4724: A Gravitationally Lensed Infrared Quasar, 1996, Astrophysical Journal, 461, 72

[5] Swinbank, A. M. et al., Intense star formation within resolved compact regions in a galaxy at z = 2.3, 2010, Nature, 464, 733

[6] Dye, S. et al., Revealing the complex nature of the strong gravitationally lensed system H-ATLAS J090311.6+003906 using ALMA, 2015, Monthly Notices of the Royal Astronomical Society, 452, 2258

[7] Dye, S. et al., A high-resolution investigation of the multiphase ISM in a galaxy during the first two billion years, 2022, Monthly Notices of the Royal Astronomical Society, 510, 3734

[8] Treu, Tommaso, Strong Lensing by Galaxies, 2010, Annual Reviews of Astronomy and Astrophysics, 48, 87

Podcast and Website: George J. Bendo

Special Guest Contribution: Steve Nerlich from the Cheap Astronomy Podcast

Additional Audio Editing: Steve Nerlich

Music: Immersion by Sascha Ende

Sound Effects: dronemachine, Greg_Surr, ivolipa, Jack_Master, jameswrowles, Mrthenoronha, newagesoup, Sample_Me, UncleSigmund, and Xulie at The Freesound Project

Image Viewer: Aladin Sky Atlas (developed at CDS, Strasbourg Observatory, France)

 

© George Bendo 2022. See the acknowledgments page for additional information.

Last update: 15 May 2022