Archive for the 'Astronomy' Category

Jul 07 2020

Mystery of the Disappearing Star

Published by under Astronomy

Stars do not just disappear – except when they do.

Using the Very Large Telescope (part of the European Southern Observatory) astronomers have been tracking a massive unstable star. The star is located in the Kinman Dwarf galaxy, which is a distant, small, and metal poor galaxy (PHL 293B – at a distance of 23.1 Mpc ). This is too far away for current telescopes to resolve individual stars, but astronomers can detect the presence of specific stars by looking at the spectral absorption lines. Between 2001 and 2011 they were monitoring a luminous blue variable star (LBV). These are massive blue stars, and this one was believed to be at the end of its life. They were able to infer temperature and other features that suggests the star was in an eruptive phase.

Then, in 2019, astronomers wanted to check back up on this star so they looked for the spectral lines in the same location of Kinman and – they were gone. The star was apparently gone. What could have happened?

The astronomers have put forth two hypotheses. The first is more mundane – if the star was in an eruptive phase, perhaps it shed a lot of its mass, rapidly becoming a much smaller and dimmer star (sometime between 2011 and 2019). This alone would not be enough to explain the disappearance, and so over this same time the star might also have been obscured by dust. This combination of factors could explain the disappearance.

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Jun 25 2020

Mass Gap Object Discovered

Published by under Astronomy

Trust me, this is cool. Astronomers have discovered a stellar remnant with 2.6 solar masses, which is within a range of mass called the “mass gap” because of the almost complete lack of such objects in that range.  This is both an astronomy mystery (how do such objects form) and a physics mystery (what forces dominate at this size). Any new data points give us clues to solve the mystery of the mass gap, so this is exciting news.

Even still, yet again I find the headlines and even the popular reporting hyping the find. The BBC headline reads, “‘Black neutron star’ discovery changes astronomy.” No, this is not going to “change astronomy,” unless you count every incremental addition of new information as changing the entire field. Also, calling it a “black neutron star”, while a possibility, is assuming only one possible conclusion. But let’s get into the interesting details.

For quick background, when stars die they leave behind a stellar remnant. When stars run out of fuel they are able to burn (which is partly determined by their mass) they no longer produce the outward pressure of fusion and so gravity takes over and they collapse. If they are large enough (8-15 solar masses) the core collapse results in a supernova. Either way, what’s left behind is a stellar remnant. Small remnants become a white dwarf, a glowing hot ember but without fusion. If the remnant is at least 1.4 solar masses the force of gravity will overcome the repulsive force among the positive proton and negative electrons and the white dwarf will collapse down to a neutron star – in simplistic terms, the electrons and protons will merge into neutrons, so the entire thing is made of neutrons.

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Jun 18 2020

Intelligent Life in the Galaxy

Published by under Astronomy

The headlines (taken from the press release) read: “New light shed on intelligent life existing across the galaxy.” But here’s the thing – I don’t think the referenced study does that at all. So what are they talking about?

The study uses their own version of the Drake Equation, which is a way of calculating how many spacefaring civilizations there are likely to be in the universe. The equation itself is correct – you consider the number of stars, the subset of those with planets in the habitable zone, the number of those who develop life, then intelligent life, then technology and multiply all that by the average lifespan of such civilizations. The equation works, as far as it goes, it’s just not terribly useful. The reason is that we don’t know the values of any of the variables. We can guess some of them, those dealing with stuff we can see, like how many planets are out there, but we essentially have no idea about any of the variables dealing with life.

The reason we have no idea is basic scientific logic – because we have one data point, Earth. Remember when we encountered the first interstellar object? That one encounter left us with no practical way to calculate how common such objects were. It could have been a one-off extremely unlikely event. But as soon as we encountered a second interstellar object, we had a rough idea how common they were. We had something to calculate.

You just can’t extrapolate from one data point. We may be the only life in the entire universe, or the universe might be teeming with life – both ends of the spectrum are consistent with our one known data point. We have no idea how common life is, how common intelligent life is, or technological civilizations, or how long they survive on average. None – really. So any numbers we put in are just wild guesses, and the errors on those wild guesses multiply.

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Apr 21 2020

The Strange Interstellar Comet

Published by under Astronomy

Is our solar system similar to other solar systems? That’s actually a complex question with many layers. We know that there are different types of stars, varying mainly on their mass and age. We have a yellow sun, but a system around a red, orange, or blue sun is likely to be very different. We also know that at different relative locations in the galaxy the composition of the gas clouds out of which stellar systems form can be very different. One specific difference is known as “metallicity” – which refers to the amount of elements heavier than hydrogen or helium. Older stars were formed before a lot of heavier elements were made, so they have lower mellacity. This feature also varies within our galaxy, with higher metallicity closer to the center. And different galaxies have different mettalicity.

But what should we expect from a stellar system with a yellow sun at a similar location in our own galaxy? If the known variables are the same, should we expect the compositions of elements to also be roughly the same? This gets to the deeper scientific question of how typical our system is. Can we assume that the rest of the universe is similar to our tiny little corner of it? To counteract the hubris of humanity in thinking that we are somehow special, scientists try to follow the principle to assume that we are ordinary. But is that assumption always correct?

How can we even answer this question for stars that are light-years away? The primary method that we use is spectral analysis  (spectroscopy) – an awesomely powerful tool that allows us to identify specific elements and chemicals simply from analyzing the light we see from it. You can do a spectral analysis in a lab on a sample, or you can do it with telescopes on distant objects. The method is actually fairly simply. You use a prism to spread out the light into its color spectrum (like a rainbow). You can then analyze the emission lines or absorption lines which are like a signature.

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Apr 20 2020

Crew Dragon Launches in May

Published by under Astronomy,Technology

Amid the current crisis there is some good news and significant progress – America is returning to crewed spaceflight after a 9 year gap. Scheduled for May 27th is the first crewed mission of the Space X Dragon capsule, which will send two astronauts to the ISS,  Bob Behnken and Doug Hurley. Technically this is the last test flight of the Crew Dragon capsule (the mission is called Demo-2). Last March the Demo-1 mission sent an uncrewed Dragon capsule to the ISS. The two astronauts will remain for an “extended” stay on the ISS, and then return in the capsule, splashing down in the Atlantic and recovered by a Space X recovery vessel.

If successful this will mark the return of America’s ability to send astronauts into orbit. It will also mark the first time a commercial company has done so, and is a significant milestone in the commercialization of space flight. The launch will be done in cooperation with NASA, lifting off from Pad 39A, which is the same one that launched Apollo and the Space Shuttle. The capsule will also be lifted to the ISS by a Falcon 9 rocket, which is also made by Space X. This is the rocket that can land again vertically and be reused.

There has been some back and forth on whether or not the Crew Dragon capsules themselves can be reused. Initially Musk predicted that the capsule could be reused many times, reducing the cost of getting astronauts into space. Then in 2018 they quietly backed away from this goal. The reason is that after a salt-water landing, it is time consuming (a year) and expensive to service the capsule for reuse. In order for capsule reuse to be practical you need a dry landing, which was the original plan of Space X. Apparently that has proven technologically difficult, so Space X is settling for salt-water landings, which means no reuse. However, the Crew Dragon capsule can more easily be refurbished and reused for Cargo Dragon missions without astronauts. Therefore, they will be used for this purpose. Space X has reused multiple Cargo Dragon capsules multiple time.

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Mar 30 2020

Building Moon Bases Using Urine

Published by under Astronomy,Technology

This is an interesting idea that will probably not be actually implemented (although not impossible) but does raise some important points. A paper explores the viability of using urea from human urine as an agent in lunar concrete. Why is something like this even being considered?

The overwhelmingly dominant factor of building anything on the Moon is that it costs about $10,000 to put one pound of anything into Earth orbit, and more to take it to the Moon (although most of the energy would be used just getting into orbit). This is why it is a high priority for NASA to reduce the cost of getting stuff into space. Elon Musk has also made this a priority and SpaceX is geared mainly toward this purpose. Even if they reach their goal of reducing the cost by 10 fold, to about $1000 per pound, that still adds up when you are trying to build an entire Moon base. One solution is to use as much native material as possible.

Let’s talk a bit about the lunar regolith. The term regolith just refers to any loose material on top of the rocks on a world’s surface. The Earth has regolith, we call it dirt, sand, or soil. The lunar regolith is the result of micrometeors pulverizing the lunar surface for billions of years. In most locations the regolith extends down 4-5 meters, but can be as deep as 15 meters in places. Because of the absence of natural erosion from wind, water, or biological activity, the lunar regolith remains sharp and pointy. So the Moon is basically covered with a deep blanket of fine but jagged dust.

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Mar 10 2020

Day Was Shorter 70 Million Years Ago

What does an extinct mollusk have to do with the Moon? This is one of those amazing science stories that ties together multiple disciplines and lines of evidence into one elegant narrative. In this case a detailed analysis of a 70 million year old mollusk shell has given scientists a critical piece of information that will help them model the Earth-Moon system.

Let’s start with the Moon – astronomers know that the Moon is moving farther away from the Earth at a constant rate, 3.82 centimeters per year. We can precisely measure this because the Apollo missions left corner reflectors on the surface of the Moon, and we can shoot lasers off those reflectors and measure the round-trip travel time. Because scientists have also precisely measured the speed of light, we can use this round-trip time to calculate the exact distance between the laser on Earth and the reflector on the Moon.

Why is the Moon moving away from the Earth? In a word – tides. Tidal forces from nearby large objects causes a bulge to form. We are most familiar with this phenomenon because of the bulge in the ocean caused mostly by the Moon (and to a lesser degree the Sun) which we experience locally as a rising and falling of the sea. The tidal bulge on the Earth is slightly ahead of the Moon in its orbit, because the Earth is spinning faster than the Moon. This leading bulge tugs slightly on the Moon, accelerating it into a higher orbit farther from the Earth. This represents a transfer of momentum from the Earth to the Moon via gravity, which not only moves the Moon farther away, but slows down the rotation of the Earth (and the conservation of angular momentum is obeyed).

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Feb 28 2020

Astronomers Detect Largest Explosion Ever

Published by under Astronomy

We can quibble about whether or not the Big Bang should be considered an explosion, or whether it happened “in the universe.” It was the expansion of spacetime that is the universe. In any case, astronomers have detected what they think is the biggest explosion (at least discovered so far) since the big bang –  in the Ophiuchus galaxy cluster, 390 million light years from us. The explosion is essentially a bubble with a diameter the size of 15 Milky Way galaxies – about 1.5 million light years across. That’s five time bigger than the previous record holder.

Astronomers first suspected something was going on when they discovered a big X-ray bubble. They report:

It was discovered in the Chandra X-ray image by Werner and collaborators, who considered a possibility of it being a boundary of an AGN-inflated bubble located outside the core, but discounted this possibility because it required much too powerful an AGN outburst.

An AGN is an active galactic nuclei – more on that below. So they initially discounted it because it was too big, but they then followed up with radio observation, and found an identical radio bubble, confirming that this was a real fossil of an ancient explosion, centered around an AGN. So what’s going on here?

Well, astronomers are not sure. The do not know exactly what may have caused some a massively energetic event. But let’s give some background on AGNs – these are supermassive black holes (SMBH) in the centers of galaxies. Most galaxies have them, including our own. But some supermassive black holes are more super massive than others – getting up to billions of solar masses. More importantly to their activity, some of the black holes are feeding, which means that gas and dust are actively swirling around the event horizon forming an accretion disc and then plunging into the incredible gravity well of the black hole. All that gravity represents an unimaginable amount of energy, and when that gas and dust falls in it swirls around at relativistic speeds – near the speed of light.

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Feb 25 2020

Marsquakes and Magnetic Fields on Mars

Published by under Astronomy

The Mars InSight lander is yielding data, and the first slew of papers reporting early results. The two big stories so far is that Mars has more seismic and magnetic activity than previously thought.

One open question is how much tectonic activity there is on Mars. Earth has at least 15 tectonic plates, all moving with respect to each other. When two plates rub up against each other, building up and then releasing energy, this is the major source of Earthquakes. Both Mercury and the Moon, which are smaller and therefore cooled much faster than Earth, have single crust plates. That doesn’t mean they have no seismic activity, because they are also shrinking as their cores continue to cool.

Mars is still a bit of an open question in terms of tectonic activity. It appears likely that Mars does have a tectonic plate system, but much simpler than Earths with fewer plates, and they are moving much more slowly. But this still can allow for some seismic activity. There are other sources of activity as well, such as shrinking and settling. Information on seismic activity from InSight was anticipated to help better understand the geological activity on Mars.

What they have found so far is:

“We identify 174 marsquakes, comprising two distinct populations: 150 small-magnitude, high-frequency events with waves propagating at crustal depths and 24 low-frequency, subcrustal events of magnitude Mw 3–4 with waves propagating at various depths in the mantle.”

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Feb 17 2020

Mainstreaming SETI

Published by under Astronomy

This weekend I was at the AAAS (American Association for the Advancement of Science) meeting in Seattle talking about science communication. The meeting often creates a pulse of science-news reporting, base on all the presentations and lectures there. One talk I didn’t get to see was by Dr. Anthony Beasley, director of the US National Radio Astronomy Observatory in Charlottesville, Virginia. He argued that the search for extraterrestrial intelligence (SETI) should “come in from the cold” and be incorporated into every aspect of astronomy. Let me go over the reasons why I completely agree.

First, doing so would be a great boost to SETI itself. For example, private funding has recently allowed a SETI project using the VLA (Very Large Array) which the project managers argue will increase the power of SETI by 10-100 fold. Taking SETI from an isolated project here and there to the mainstream of astronomy would certainly greatly magnify the power of SETI searches, and therefore increase the probability of achieving a positive result.

Further, as Seth Shostak has pointed out to us during interviews on the SGU, SETI research does a lot of non-SETI astronomy. Of you are scanning the skies with radio telescopes looking for signals that may be intelligent in origin, you are also gathering a lot of information that can be used for other purposes. So even if SETI never detects such a signal, the effort will not have been wasted. A lot of non-SETI astronomy will still have been done. The broader point is that, by combining SETI with other projects, astronomers are efficiently using equipment and data. What this means is that the question of SETI vs other projects is a false dichotomy. We can do both.

But the biggest question in all of this is – is SETI itself valuable? There are two criteria that are usually brought to bear in answering this question. Mostly people focus on the probability of detecting an ET signal, with critics of SETI arguing that it is probably too small to be worth the effort of searching. Defenders of SETI often focus on the other criterion – the value to humanity if we did detect a signal. In essence SETI is like playing the lottery – the probability of winning is low but the potential benefits are high. How do we balance these two things out?

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