Archive for the 'Astronomy' Category

Apr 03 2018

Fermi vs Drake

Published by under Astronomy

In the world of Dune, human civilization about 10,000 years in the future had colonized the galaxy, with an empire spanning a “million” worlds. There were no aliens to get in our way, so once we had the technology for interstellar travel, we spread out. The first Dune novel was published 15 years after Fermi made his famous observation – essentially, if aliens exist, where are they? Why haven’t they colonized the galaxy like the humans in Dune?

More than half a century later, the Fermi Paradox remains a hotly debated mystery. One might also invoke the Drake Equation in this discussion. I often hear the Drake Equation dismissed as pseudoscience, but it is just a thought experiment. It is an equation that can be used to calculate the number of technological civilizations in the universe by plugging in all the relevant variables – number of stars, then planets, then planets with life, than life that evolved intelligence, etc.  The only thing that can be considered pseudoscience is plugging in numbers that are just guesses and pretending they are scientific estimates.

The Drake Equation

We have started to make progress informing the variables in the Drake Equation, however. Astronomers have a pretty good handle on how many stars there are in the observable universe. Current estimates are that there are about 2 trillion galaxies in the observable universe, with an average of about 100 million stars per galaxy – 200 quintillion stars. We could be off by an order or magnitude or two, either way that is a massive number.

However, many people are interested in the subquestion – how common is intelligent life in the Milky Way galaxy? Therefore, how many stars are there in the Milky Way?  Estimates vary there as well, but it is on the order of 100 billion (could be several hundred billion).

After estimating the number of stars, further estimates in the Drake Equation get immediately dodgy. What we need to know next is how many stars have planets, and what is the typical distribution of planets by size and distance from their host star. In other words, how many stars have planets that can potentially host life? This is further complicated by the fact that we can only guess at how adaptable “life” is. Can life develop under the ice of large moons of gas giants? How about in the upper atmospheres of those gas giants?

It is easier, therefore, to answer the question – how many Earth-like planets are out there?

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Mar 29 2018

Galaxy Without Dark Matter

Published by under Astronomy

One of the cool things about astronomy is that the universe is a huge place, and we can look in any direction and see lots of stuff. Current estimates are that there are about 2 trillion galaxies in the visible universe. Galaxies vary in size, but have on the order of hundreds of billions of stars.

What this means is that even if a phenomenon occurs only in one in every billion galaxies, there are still two thousands of them out there for us to find. Or even a one-in-a-million star will occur hundreds of thousands of times in our own galaxy. So the more we look, the rarer and rarer stuff we will find.

Recently astronomers happened upon one such rare occurrence – a galaxy that appears to be devoid of dark matter. That’s not supposed to happen, so if it is confirmed by longer study will have significant implications for our understanding of the universe.

Dark matter is material that has a gravitational effect that we can observe, but does not radiate and so is “dark”. The existence of dark matter was first proposed by Fritz Zwicky to explain the apparent rotation of observed galaxies. Based on Newton’s gravitational equations, we can calculate how fast a galaxy should rotate based on how much mass it contains. Another way to look at this, if we observe how fast a galaxy is rotating, we can calculate how much mass it should contain. If it contained less than the needed mass, the stars would be flung away by their observed velocity.

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Jan 11 2018

Fast Radio Bursts – Still Not Aliens

Published by under Astronomy

This is a (sort of) follow up to my previous post. Fast Radio Bursts (FRBs) are a legitimate astronomical mystery, and very interesting. They are very brief (30 microseconds to 9 milliseconds) and very powerful bursts of radio waves. To date about 30 FRBs have been detected. Most of these FRBs are one-offs – they occur once and never repeat (at least so far). There is one exception, however, FRB 121102 (more on that below).

What do we know about FRBs so far? They are isotropic, which means they occur all over the sky. They are not concentrated in the galactic disk. This by itself implies they are extragalactic. But also analysis of the radio bursts indicate that they have traveled through intergalactic plasma, for billions of light years. So they must also be incredibly powerful. The radio waves are broadband, so they are spread throughout the radio wavelengths. They are also highly polarized, which means they were aligned at their creation with a strong magnetic field.

Because they are radio bursts, they are studied by radio astronomers, which includes SETI astronomers, whose primary mission is to survey the sky for possible alien communications. In an SGU interview with SETI astronomer Seth Shostak he indicated that SETI does a lot of non-ET-related astronomy. This is a good example of that – they are helping to detect and analyze FRBs, including analysis of FRB 121102.

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Jan 09 2018

Tabby’s Star Mystery Partly Solved

Published by under Astronomy

It’s not aliens.

So far, no astronomical mystery has turned out to be aliens, although this hypothesis seems to come up every time. The first detections of signals from pulsars were named LGMs for “little green men.”

I’m not really criticizing this – part of me wishes the mystery will turn out to be evidence of an alien technological civilization. I always think of how plausible that is for an explanation. But still it should be last on the list. Chances are overwhelming that we are just seeing some new or unusual natural phenomenon. It’s a big complex universe out there.

In this case astronomers found a genuine mystery – a star that dimmed and brightened over time to a degree never seen before. The star has the designation KIC 8462852, and has been nicknamed “Tabby’s Star” after the astronomer who first described it, Tabetha Boyajian (she actually led a team of 200 astronomers involved in the work).

The intensity of the light coming from the star, which is a little bigger and 4.7 times brighter than our sun and is about 1300 light years away, dims at irregular intervals by as much as 22%. This could not be caused by a planet passing in between us – even a Jupiter-sized planet would only block about 1% of the light from the star. And what’s with the irregular period? Dimming from an object in orbit should be very regular.

The best hypothesis was that a swarm or cloud of something was blocking the light. It would have to be a big and dense cloud, however. This hypothesis had problems also, however, because such a cloud should be heated up and glowing in the infrared, but we don’t see it.

The “swarm” idea sparked the notion of a Dyson swarm, which is a hypothesized high-tech structure surrounding a star used to capture the light for energy. An advanced civilization, for example, could power themselves with either a large single structure of solar cells, or a swarm of smaller ones.

No scientists really took the alien megastructure hypothesis seriously, even though it could not be entirely ruled out. It was just way too early to get excited, and it was overwhelmingly likely that a natural explanation was to be found. But scientists love a mystery in any case, and whatever was going on around Tabby’s star was likely to be new and interesting.

What astronomers needed was a lot more data. So Boyajian and others started a kickstarter campaign to fund the telescope time they would need to gather that data. The campaign was successful, exceeding their needed $100,000. Last week they published the result of their analysis and…no aliens.

What they did was look at the different wavelengths of light to see how they were dimmed. If the swarm that is causing the dimming is comprised of solid objects, whether rocks, planetary debris, comets, or solar panels, then all wavelengths should be dimmed equally. That’s not what they found. They found that different wavelengths were dimmed to different degrees at different times.

That is what you would expect to find if the cloud (circumstellar material) blocking the light were comprised of very tiny particles (smaller than a micron), like dust. So that is what they concluded – there is a dense dust cloud around Tabby’s star blocking the light from our perspective. This also makes sense in terms of the variable periods, because different densities in the cloud could cause random fluctuations in the amount of light blocked.

But of course now astronomers just have a new mystery – what caused this massive fine dust cloud around Tabby’s star? Comets are very dusty, and a dust cloud like this could result from a comet – but it’s a lot of dust. It’s also probably close to the star, which means it is also probably a recent phenomenon as a dust cloud would likely not survive long that close to a star that bright. This also still doesn’t explain the lack of an infrared glow from the cloud.

The results also don’t rule out that the star is dimming and brightening on its own, and not just being blocked from view. And of course, some hopefuls have pointed out that it could be a swarm of alien nanobots or similar microscopic technology. Sure.

There is still more science to be done here, but this latest result does add a significant piece to the puzzle. It’s also cool that the research was crowd-funded. That’s a great way to get private citizens involved in science, and to fund more science. That may, in fact, be the bigger story here. Yeah for crowdfunding cool science.

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Dec 15 2017

Saturn’s Rings Are Younger Than Previously Thought

Published by under Astronomy

The gorgeous rings of Saturn are one of the most dramatic features of our solar system, and certainly a favorite of any backyard astronomer. Are they, however, a fixture that have been present for the majority of the life of our solar system, or are they a recent addition?

Of course we have no observations from millions or billions of years ago, so we can only infer their probable age. Up until recently astronomers believed they were probably ancient because the large collisions that likely produced them would have been far more likely in the early crowded solar system. However – recent evidence from Cassini has changed that conclusion.

The Cassini probe made detailed observations of Saturn and its rings for years, until it plummeted into the planet this September. Scientists are still analyzing all the data it sent back home. Two lines of evidence suggest that the rings of Saturn are far younger than previously suspected.

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Oct 20 2017

Making Oxygen on Mars

Published by under Astronomy,Technology

Mars baseAt some point humans will travel to Mars. It seems inevitable, the only question being when that will happen. Optimists like Musk think it will happen before mid-century, but that may not be realistic. There are significant logistical hurdles without clear solutions.

Some argue, and I agree with this strategy, that we should focus first on a moon base. The moon is a lot closer, which solves many problems right there. But otherwise it would have many of the same challenges as Mars, and so if we develop a base on the moon we can use what we learn to be better able to tackle Mars. Further the moon can be a literal launching pad for Mars.

While Mars has some extra challenges, it may have some advantages as well over the moon. NASA experts have observed that Mars has just enough of an atmosphere to be a problem. It has 1% of the pressure of Earth, which means for astronauts it is functionally the same as a hard vacuum. You still need pressure suits, pressurized living spaces, and you need a supply of air to breath.

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Oct 19 2017

More Gravitational Waves

Published by under Astronomy

neutronStar_drupal_withNOcaptionThe winner of the Nobel prize for physics was the detection of gravitational waves. These are extremely subtle ripples in spacetime caused by massive cataclysmic events, such as black holes colliding. These ripples were predicted by Einstein, who thought we may never be able to detect them because they would be so unbelievably tiny.

How tiny?  LIGO (Laser Interferometer Gravitational-Wave Observatory), the device used to detect the waves, can detect changes as small at 10 -22 meters. Graviational waves detected so far have had an amplitude of 10 -18 meters, smaller than the radius of a proton.

How is that possible? That is where the interferometry comes in. LIGO uses a laser split into two beams that will travel for 8 Km and then reflect off mirrors and come back to the same detector. The two beams have traveled the exact same distance so that they are in phase, or at least they can be calibrated to be exactly in phase, meaning that the peaks of the waves line up. When a ripple in spacetime comes through, the length of the two arms (which are at 90 degree angles to each other) will change slightly, bringing the two beams out of phase. That slight phase shift can be detected and measured.

Prior to winning the Nobel prize LIGO had detected four gravitational waves wash over it. This was considered enough of a confirmation of the technology and science to award the prize.

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Oct 10 2017

Half the Matter in the Universe Just Found

Published by under Astronomy

filamentsBy now most people are familiar with dark matter – that mysterious substance which has gravity but otherwise does not seem to interact with the normal matter with which we are most familiar. About 27% of the stuff (matter and energy) in the known universe is dark matter, 68% is dark energy, and only about 5% is made of known particles (baryons – protons, neutrons; leptons – electron; and more exotic particles).

We currently don’t know what dark matter is. We know it’s there because we can see its gravitational effect, first noticed because galaxies spin faster than they should. Based just on the gravity from stuff we can see, galaxies should be flying apart. They stick together because there is significantly more gravity than we can account for. There must be additional matter we can’t see, or dark matter.

It is perhaps less well-known that we also haven’t found about half of the normal matter that should exist in the universe. Even if we just consider that 5% that is made of standard particles, about half of it is missing. That is – until now, if recent reports are accurate.

This really wasn’t much of a mystery (not like dark matter) – astronomers suspected that the missing matter was present in the form of diffuse gas between galaxies. There is a lot of space out there, and even a wispy vapor could contain a lot of particles, as much as is contained in all the visible galaxies. The problem is, this thin gas is too wispy to see with conventional means.

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Sep 15 2017

Cassini’s Dramatic End

Published by under Astronomy

Saturn- CassiniThe Cassini probe to Saturn has been considered one of the most successful space missions in history. Today it will plunge into the upper atmosphere of Saturn. As the atmosphere gets thicker on its way down the probe will begin to tumble from the turbulence, until it is ripped apart by the violent forces and finally melts in the intense heat of the gas giant. (As I am writing this there are just 30 minutes left.)

This is the intended fate of the probe. It was launched in 1997, took seven years to get to Saturn, and has been studying the planet and its moons for 13 years. It has dramatically improved our knowledge of the Saturn system. Cassini was the first probe to orbit Saturn. Prior to that, Pioneer and Voyager had performed flybys, which gave us quick glimpses but did not allow for extended study.

In addition to being a feat of science and engineering, Cassini surpassed expectations. Its original mission profile was for four years. It was able to have two mission extensions, for a total of 13 years. Now it is almost completely out of fuel – its mission is over.

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Aug 29 2017

40 Years of Voyager

Published by under Astronomy

voyager1_highOn August 20th 1977 Voyager 2 was launched. On September 5th Voyager 1 followed. The reason 2 launched before 1 is because V1 was on a faster trajectory and would arrive at Jupiter several months before V2, and NASA felt it would be easier not to have to explain endlessly to the media why V2 was arriving before V1. At present V1 is 12,959,246,289 miles from Earth, and V2 is 10,657,559,202 miles.

Voyager 1 is the farthest human made object from the Earth. If our civilization collapses tomorrow, the Voyager probes would be the longest surviving artifacts of our existence.

If you do not remember the Voyager missions, then think of what it was like for Horizon to fly by Pluto. Pluto went from a fuzzy blob to a detailed alien world. The Voyager missions were the same, except times four. This was our first closeup look at Jupiter, Saturn, Uranus and Neptune. It was our first closeup look at the large moons of Jupiter – Io, Ganymede, Europa and Callisto. We discovered even more smaller moons of Jupiter and Saturn. We discovered volcanic activity on Io, and that Jupiter has rings of its own.

Our knowledge of the outer solar system exploded, and we were rewarded with seemingly endless gorgeous pictures of these giant worlds and their companions.

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