New Infra-red Search for sub-Brown Dwarfs Planned
Brown dwarfs are notoriously hard to find. It’s not so bad when they are first born: They come into the Universe with a blast, shedding light and heat in an infantile display of vigour. But within just a few million years, they have burned their available nuclear fuels, and settle down to consume their leaner elemental pickings. Their visible light dims considerably with time to perhaps just a magenta shimmer. But they still produce heat, and the older they get, the more likely that a direct detection of a brown dwarf will have to be in the infra-red spectrum.
This doesn’t make them much easier to detect, though, because to catch these faint heat signatures in the night sky, you first need to have a cold night sky. A very cold night sky. Worse, water vapour in the atmosphere absorbs infra-red light along multiple stretches of the spectrum. The warmth and humidity of the Earth’s atmosphere heavily obscures infra-red searches, even in frigid climates, and so astronomers wishing to search in the infra-red either have to build IR telescopes atop desert mountains (like in Chile’s Atacama desert), or else resort to the use of space-based platforms. The downside of the latter is that the telescopes tend to lose liquid helium supplies rather quickly, shortening their lifespan considerably compared to space-based optical telescopes.
The first major sky search using a space telescope was IRAS, back in the 1980s. Then came Spitzer at the turn of the century, followed by Herschel, and then WISE about five years ago. Some infra-red telescopes conduct broad searches across the sky for heat traces, others zoom in on candidate objects for closer inspection. Each telescope exceeds the last in performance, sometimes by orders of magnitude, which means that faint objects that might have been missed by early searches stand more of a chance of being picked up in the newer searches.
The next big thing in infra-red astronomy is the James Webb Space Telescope (JSWT), due for launch in Spring 2019. The JSWT should provide the kind of observational power provided by the Hubble Space telescope – but this time in infra-red. The reason why astronomers want to view the universe in detail using infra-red wavelengths is that very distant objects are red-shifted to such a degree that their light tends to be found in the infra-red spectrum, generally outside Hubble’s operational parameters (1). Essentially, the JWST will be able to see deeper into space (and, therefore, look for objects sending their light to us from further back in time when the first stars and galaxies emerged).
One of the advantages of this shift into the red is that this extremely powerful telescope will also have the capability to seek out new brown dwarfs. Precious telescope time is currently being allocated to various teams of astronomers wanting to observe parts of the sky when the JSWT is eventually operational. Two recent announcements about these allotted slots involve brown dwarfs. The first is a closer look at a young low-mass brown dwarf which lies relatively close to the Sun, by stellar standards, and is a member of a 200-million-year-old group of stars called Carina-Near. This particular object is known as SIMP0136 (2).
SIMP0136 is a free-floating sub-brown dwarf, so its light is not obscured by the presence of a parent star. This makes it a lot easier to study, providing the opportunity to analyse the components of its cloudy atmosphere. Brown dwarfs cover a reasonably broad swathe of masses, generally thought to be from about 13 Jupiter masses (mJ) up to about 80 mJ (at which point they light up into red dwarfs). SIMP0136 lies at the very lowest end of this brown dwarf range of masses, at about 13 mJ (3), which also places is at the top end of the next set of objects – the sub-brown dwarfs. Technically, at this lowly mass, it could be considered a planetary mass object rather than a stellar object. Sub-brown dwarfs are, in effect, massive gas giant almost-stars. We’re likely to find out a lot more about the properties of these objects as a result of this study.
The second JSWT project announcement aims to study the NGC 1333 stellar nursery, located in the constellation of Perseus (2). This nebula contains a great many birthing stars and young brown dwarfs and is thought to also contain an abundance of sub-brown dwarfs. It’s difficult to spot sub-brown dwarfs at the best of times, but the search for them is all the more difficult here because of the obscuring clouds of gas and dust within the nebula. A powerful infra-red search should allow them to pop out from their cosmic hiding place:
“Stars and planets that are just forming lie hidden behind cocoons of dust that absorb visible light. (The same is true for the very center of our galaxy.) However, infrared light emitted by these regions can penetrate this dusty shroud and reveal what is inside.” (1)
Not only is this a critical factor when trying to search for free-floating planetary mass objects within nebulae, but this issue also underpins my hypothesis seeking to explain the current lack of detection of distant planets in our own solar system.
There is a persistent and – arguably – growing body of indirect evidence for the existence of one or more Planet X objects lying in very distant locations in our own solar system. Yet, such objects seem to evade direct detection. This is, of course, very frustrating for the astronomers seeking out Planet X (or Planet Nine as some have renamed it (4)), and provides grist for the mill for sceptics wishing to discredit the entire concept. For a few years, I have argued that localised nebulae may form around planetary mass objects located outside of a star’s heliopause. Without the wafting action of the solar wind, and other dynamical processes driven by a star’s proximity, interstellar dust may accumulate slowly around an externally located massive planet. The planet then becomes embedded within a dusty shroud, obscuring it from view in the visible spectrum (5).
This means that searches using normal optical telescopes, like the Subaru telescope in Hawaii, are bound to fail to find Planet Nine. Furthermore, infra-red sky searches like WISE might pick up an infra-red signal, but efforts to then confirm the presence of a ninth planet using standard telescopes would also fall short (or, at least, detect a faint, fuzzy mass, rather than a distinct object). So, the infra-red signal (and commensurate visible fuzz) would be attributed to a different phenomenon.
Could the powerful JSWT change matters? I don’t believe so. The telescope would need to be specifically trained in on candidate objects. Without candidate objects to examine (thus far there is exactly none) then precious observation time using the telescope will not be allocated to a Planet X project. Without a wider appreciation of the potentially variant properties of externally located planets, the status quo will remain in place: Strong indirect evidence of a massive perturbing influence, but zero prospect of actually spotting it.
Written by Andy Lloyd, 7th January 2018
1) JWST “Webb vs Hubble Telescope” NASA, https://jwst.nasa.gov/comparison_about.html
2) Leah Ramsay “NASA’s Webb Telescope to Investigate Mysterious Brown Dwarfs” 4th January 2018 https://www.nasa.gov/feature/goddard/2018/nasa-s-webb-telescope-to-investigate-mysterious-brown-dwarfs with thanks to Monika
3) Carnegie Institution for Science Press Release “Surprise! When a brown dwarf is actually a planetary mass object” 9th May 2017 https://carnegiescience.edu/news/surprise-when-brown-dwarf-actually-planetary-mass-object
4) K. Batygin & M. Brown “Evidence for a Distant Giant Planet in the Solar System” 20th January 2016, The Astronomical Journal, Volume 151, Number 2, http://iopscience.iop.org/article/10.3847/0004-6256/151/2/22
5) Andy Lloyd “The Cumulative Effect of Intermittent Interstellar Medium Inundation Upon Objects In The Outer Solar System” 02/2016, DOI: 10.13140/RG.2.1.5112.5526, https://www.researchgate.net/publication/293488683_The_Cumulative_Effect_of_Intermittent_Interstellar_Medium_Inundation_Upon_Objects_In_The_Outer_Solar_System, and an updated version (22/2/16) is available here: https://www.academia.edu/21700220/The_Cumulative_Effect_of_Intermittent_Interstellar_Medium_Inundation_Upon_Objects_In_The_Outer_Solar_System