Hidden black holes, Mars Magnetic field, banded brown dwarfs, & special guest Andreas Faisst

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Today we are going to be joined by CalTech scientist Andreas Faisst, who is the US lead principal investigator for ALPINE, a 70-hour program using ALMA to study the early universe. We recently discussed his team’s latest paper on the formation of spiral galaxies in the early universe, and today he will be joining us to provide a deeper dive into the cool new science.

Before we do that, however, let’s take a look at the news.

In our top news story of the day, we learn that black holes may be closer than we thought. Quite by accident, a team of double star observers has found a black hole just 1000 light-years from earth. While studying two stars that can readily be seen in dark skies with the unaided eye, the team found their motions required a third object – an invisible object – an object that doesn’t appear at all and matches what we’d expect from a black hole. One of the two stars in this system appears to orbit an unseen companion every 40 days, while the outer star orbits both these objects. This study was led by Thomas Rivinius, and he used the ESO 2.2m telescope at La Silla in Chile. This apparent black hole is well-behaved; it isn’t cannibalizing its companions, it isn’t flaring in X-Ray, it isn’t doing anything other than hanging out and using its 8-solar mass worth of gravity to move around its companions.

In a way, this was a lucky find. This team’s careful photometry was spread out over time and was initially designed to measure the much slower motions of the outer star in the system. While this did let them catch all the needed position measurements to sort all 3 orbits, other systems haven’t been so polite. The team now thinks that noise in several other double star systems may be consistent with the double stars actually being 3 objects.

Back when I was in college, a guest speaker said that when we look at the stars, 4 out of every 3 stars is a binary. For those of you not catching the joke, this was referring to how so many things we look at initially appear as individual stars, but turn out to be binary stars with enough observing. Think you have 3 stars in your binocular view? Well, grab a telescope and you may discover those 3 stars are 5, with 2 sets of 2. Today, there is a lot of debate on exactly how many stars are binaries, but it looks like those arguments are going to get more complex as we have to also ask, which systems are hiding dark objects? Project lead author Thomas Rivinius puts it this way: “There must be hundreds of millions of black holes out there, but we know about only very few. Knowing what to look for should put us in a better position to find them,” says Rivinius. Co-author Baade adds that finding a black hole in a triple system so close by indicates that we are seeing just “the tip of an exciting iceberg.”

From a distant triple system, we now turn to the 4th rock from the Sun. In a new paper in the journal Science Advances, a team led by Anna Mittelholz has used data from the MAVEN spacecraft to determine when Mars had a magnetic field. The verdict is: 4.5-3.7 billion years ago, a compass would have helped you get around the red planet. To get a magnetic field, a world needs to have a liquid mantle capable of moving charged particles in a dynamo. Or, put differently, things happen that we don’t really understand and have named a dynamo, and a magnetic field is generated. Really – we don’t totally understand the generation of magnetic fields in planets, but we know that a liquid material is required. When that magnetic field is in place, any rocks that form with the correct magnetically sensitive materials will align their minerals along that magnetic field, essentially recording its presence and orientation. Using MAVEN data, the team was able to measure a magnetic field coming from the Lucus Planum lava flow on Mars that is believed to have formed 3.7 billion years ago. This is the youngest fossilized magnetic field to be found, and regions created 3.9 billion years ago show no evidence of that martian dynamo indicating we’re narrowing in on the shutoff time.

This work is published today, and we haven’t had a chance to fully read the paper yet, but one cool thing not mentioned in the press release is this magnetic field would have coincided with the same period of time when Mars had water and an atmosphere, and it would have helped make Mars an even more habitable place than we already knew it was. Now more than ever, I’m eager to go fossil hunting on Mars.

Our final story of the day takes us scientifically to a place between stars and planets; this is the land of Brown Dwarfs. These failed stars form like stars, but just don’t have enough mass to maintain nuclear reactions that burn regular hydrogen, and instead only have a fitful burning of tritium and deuterium early in their lives. With masses 13-80x that of Jupiter, these objects are physically the size of a gas giant, and new observations from a team at CalTech find that these objects may also have a banding pattern not too different from what we see in gas giants. While studying Luhman 16A, a brown dwarf in a close binary just 6.5ly away, team scientists saw fluctuations in brightness consistent with the presence of clouds. The initial observations were done with the Spitzer space telescope and looked at this object in the infrared. New observations with the ESO VLT in Chile looked at the starlight’s polarization and found that it is consistent with the clouds being in smooth bands instead of it being patchy large clouds. They can’t tell how many bands there may be, that is left for the artist, but this does tell us that these failed stars have weather like planets. According to co-author of this study, Julien Girard of STScI, “these storms can rain things like silicates or ammonia. It’s pretty awful weather, actually.”

This work appears in the Astrophysical Journal and is led by Maxwell Millar-Blanchaer, who points out, “This is the first time [polarimetry has] really been exploited to understand cloud properties outside of the solar system.” Here is to hoping more of this kind of big science can be done with the ever-growing number of big telescopes being built around the world. When this happens, we’ll bring it to you right here on the Daily Space.

Learn More

Hidden Black Holes

Press release from the European Southern Observatory
“A Naked-Eye Triple System with a Nonaccreting Black Hole in the Inner Binary,” Thomas Rivinius et al., 2020 May 6, Astronomy & Astrophysics.

Ancient Mars Magnetic Field

Press release from the Planetary Science Institute
“Timing of the Martian Dynamo: New Constraints for a Core Field 4.5 and 3.7 Ga Ago,” A. Mittelholz et al., 2020 May 1, Science Advances

Banded Brown Dwarfs

Press release from CalTech
“Detection of Polarization Due to Cloud Bands in the Nearby Luhman 16 Brown Dwarf Binary,” Maxwell Millar-Blanchaer et al., 2020 May 5, Astrophysical Journal

Guest Dr Andreas Faisst