More space news!

[tkdguy]

It would make a good novel, in any case.

[megaplayboy]

Well, if true, those guys would be too far ahead to bother communicating with us. The gap in tech capability is likely millenia, not centuries. They would literally have to be billions of times more powerful and knowledgeable than us.

[Cancer]

The paper is to appear in MNRAS, but the preprint is here. Colors and spectra indicate an F3V star (surface temperature ~6750 K, compare the Sun's ~5800 K) with a rotation speed of about 84 km/s (nothing special for stars like that). Distance about 455 parsecs. The bright component seems to have an M dwarf companion about 900 AU away; that's close enough to mess with the orbits of things going around the F star, but not close enough to mess with the F star directly.

 

Interesting Bizarre.

[L. Marcus]

... An alien Dreadnought, maybe?

[Cancer]

Whatever it is, it blocks up to 15-20% of the light of the star for days to weeks at a stretch, from our point of view. And it doesn't radiate in the infrared.

[Cancer]

BTW, the title of the preprint paper is "Planet Hunters X: Where's the Flux". "Planet Hunters" is the citizen-science program to recruit folks to eyeball the Kepler light curves, and I think "X" is a Roman numeral for the paper in a series. The rest of the title is just a barely-plausible phrase that yields the WTF acronym.

[L. Marcus]

Hur hur hur ...

[Christopher]

Whatever it is, it blocks up to 15-20% of the light of the star for days to weeks at a stretch, from our point of view. And it doesn't radiate in the infrared.

Odd radiation in the IR spectrum is what we expect a Dyson type object to emit. Something of this size/coverage lacking it is odd indeed.

 

But saddly this is propably the bigest lead towards extraterestial life we have found since the start of SETI/space programm in general.

[Cancer]

I wonder how intently the radio telescopes are observing this system at the moment.

[Old Man]

Okay someone is going to have to explain to me how Kepler works.  Stars dim as planets pass in front of them, I get that.  But doesn't the system have to be edge on to us in order to observer that?  Are we just not seeing systems where we are close to the orbital axis?  And if Kepler's only been running for a few years, how do we observe planets with orbital periods greater than that?  Are we missing those planets too?

[Cancer]

Yup.

 

They chose a field (in Cygnus, near the galactic plane) where the camera can get 150,000 or stars. The only exoplanets you discover are those in orbits edge-on to you. But the photometry is good to a few parts in 10^5. And you read out every 6 seconds, coadding into either 30 second or half-hour "cadences" and downlink those. Rotate the spacecraft every so often, so as to eliminate certain instrumental artifacts.

 

The main mission is over, having lost the second reaction wheel a bit more than a year ago, so it cannot maintain the pointing needed for the photometric precision.

 

Actually, direct imaging (and gravitational microlensing) are your only hope for systems that aren't edge-on, really. Even radial velocities have the cosine theta effect.

 

There isn't a good solution for long-period systems. Jupiter's 12-year orbit period is within the detection possibilities now, since we've had the tech to see the solar reflect velocity due to Jupiter since the early-to-mid 1990s. But Saturn with its 30-year period, not yet. I think we can detect that velocity, but we need another decade of observations to see the velocity pattern start repeating.

[Old Man]

So what percentage of planets is Kepler actually able to detect at this point?  5%?  Less?

[Christopher]

So what percentage of planets is Kepler actually able to detect at this point?  5%?  Less?

We mostly care for exoplanets in the habitable zone. Thier orbits tend to a be a bit shorter then Jupiter or Saturn. Earth too mars more likely, wich have 1-2 (earh) years orbital periods.

Gas giants are kinda boring when searching for extraterestial life.

[Cancer]

So what percentage of planets is Kepler actually able to detect at this point?  5%?  Less?

Stealing an equation from a book (specifically Exoplanets, edited by Sara Seager, p. 57) ...

 

probability of seeing a transit ~= 0.005 * R*/Ro * AU/a

 

where R* is the radius of the star, R0 is the current radius of the Sun, a is the size of the orbit, and AU is astronomical units. That expression is an approximation for the case where the orbit eccentricity is small and the planet is much smaller than the star.

 

So now you have to integrate over all stellar radii of interest (and that's a function both of stellar mass and stellar age) and all orbit sizes you can hope to see a repeat (so you can turn that again into stellar mass and orbital period). Given a stellar mass function and a table of stellar evolution models one could do that numerically, though it would be a PITA.

 

So assuming a star like the Sun, then you see 0.5% of planets in 1 AU orbits, 5% of planets in 0.1 AU orbits, and if you were to wait another dozen years you'd see 0.05% of planets in 10 AU orbits. (You have to wait because the orbital period of a planet in a 10 AU orbit is just under 32 years).

[tkdguy]

New record for American astronauts: http://news.yahoo.com/astronaut-scott-kelly-sets-u-record-time-spent-105812849.html

[Old Man]

So assuming a star like the Sun, then you see 0.5% of planets in 1 AU orbits, 5% of planets in 0.1 AU orbits, and if you were to wait another dozen years you'd see 0.05% of planets in 10 AU orbits. (You have to wait because the orbital period of a planet in a 10 AU orbit is just under 32 years).

If you see one planet, there are 200 more that you don't see? So planets are like... roaches?

[L. Marcus]

A bit harder to crush.

[Cancer]

Nor do they breed as quickly.

[tkdguy]

A visitor at Halloween:  http://finance.yahoo.com/news/nasa-just-discovered-massive-asteroid-222320164.html

[Cancer]

A visitor at Halloween:  http://finance.yahoo.com/news/nasa-just-discovered-massive-asteroid-222320164.html

Link to a Java-based orbit visualization tool Use the sliders to control viewing angles and zoom, and buttons to run (or step) forward and backwards in time.

[DShomshak]

November's Scientific American has an article about the Dark Energy Survey, a program to map hundreds of millions of galaxies in hopes of measuring cosmic expansion more precisely and maybe ruling out some of the possible explanations. The article summary goes:

 

"Something is causing the expansion of the universe to speed up--but what? Scientists have proposed that a force called dark energy is behind the acceleration or, alternatively, that current understanding of gravity must be modified. If dark energy is the culprit, at least two explanations are possible.

 

"A new project called the Dark Energy Survey (DES) will aim to solve this mystery by studying the history of cosmic expansion and the extent to which dark energy may have stymied the clumping together of galaxies throughout space.

 

"It will tackle these questions in four ways--through observing supernovae, the signatures of primordial sound waves, gravitational lensing (the bending of light by matter in the universe) and clusters of galaxies."

 

There's also a short article about a search for stars collapsing directly into black holes in nearby galaxies. The astronomers are watching for red supergiant stars that just vanish, without going supernova. They already have a few candidates.

 

Dean Shomshak

[Cancer]

Certainly behind a subscriber wall, but ...

 

A disintegrating minor planet transiting a white dwarf

 

Debris orbiting a white dwarf. 4.5 hour period (so it's really close in ... hmm ...) and the transit profiles are ratty, so the transiting objects probably have trails of dust.

[L. Marcus]

My imagination paints a vivid picture of the remnants after a truly epic space battle in a galactic war.

[Cancer]

My immediate reaction is, what are they doing there? Assuming a white dwarf mass of 0.7 solar masses (pretty typical), then that orbital period implies an orbit size of 0.0072 AU. That is 1.55 solar radii. While that is quite safely larger than the white dwarf, it is much much MUCH smaller than the red giant which cast off its envelope to become the white dwarf. So to me it's a WTF situation of how that solid object got into that tiny orbit after the red giant envelope was dispersed.

[L. Marcus]

Space battle!