One billion stars precisely mapped

[Streetwind]

This is actually a spacecraft/mission that I see almost never mentioned here on the forums for some reason... yet it has been quietly working away at its task, and now, the first results are in.

ESA's Gaia spacecraft, sometimes nicknamed the Billion Star Observatory, is an astrometry satellite launched in 2013 and currently sitting at Earth-Sun L2. it has now returned enough data for a new map of the Milky Way to be published. A map made out of 1,142,000,000 stars, in full 3D, each with its position and its brightness determined with extreme precision. It is the largest all-sky survey ever performed in the history of mankind... and Gaia is only 14 months into its 5-year primary mission.

Because Gaia wants to do more than just position and brightness. It wants to map relative movements and distances, too. Already, two million stars have their relative movements characterized in the current dataset, but that's just the beginning. With each month that passes, more and more stars will reach the point where there's enough data to derive their movements from. Also, Gaia is expected to chance across tens of thousands of previously unknown exoplanets, comets, qasars and other astronomical objects along the way. Needless to say, a lot of astronomers are very excited by this.

 

Now, some disclaimers: Gaia cannot map the entire Milky Way, due to being inside it - a lot of the galaxy actually blocks itself from view. Additionally, there are limits to the minimum brightness of stars that it can reliably track. In fact, it is expected that Gaia will map "only" around 1% of the entire contents of the galaxy. I say that in quotation marks, because that's still far more than any other single instrument has ever detected.

Edited September 15, 2016 by Streetwind

[kerbiloid]

They should upgrade to 64 bit. One billion more - and they face an overflow.

[Diche Bach]

Nice! So, something like 0.1 to 0.5% of the galaxy has undergone a "preliminary" survey. 

I don't put it that way to degrade the achievement, but rather to highlight the marvel of it, and the wonder of what lies ahead for us, but especially for generations as yet unborn.

Edited September 15, 2016 by Diche Bach
numbers

[PB666]

6 hours ago, Streetwind said:

This is actually a spacecraft/mission that I see almost never mentioned here on the forums for some reason... yet it has been quietly working away at its task, and now, the first results are in.

ESA's Gaia spacecraft, sometimes nicknamed the Billion Star Observatory, is an astrometry satellite launched in 2013 and currently sitting at Earth-Sun L2. it has now returned enough data for a new map of the Milky Way to be published. A map made out of 1,142,000,000 stars, in full 3D, each with its position and its brightness determined with extreme precision. It is the largest all-sky survey ever performed in the history of mankind... and Gaia is only 14 months into its 5-year primary mission.

Because Gaia wants to do more than just position and brightness. It wants to map relative movements and distances, too. Already, two million stars have their relative movements characterized in the current dataset, but that's just the beginning. With each month that passes, more and more stars will reach the point where there's enough data to derive their movements from. Also, Gaia is expected to chance across tens of thousands of previously unknown exoplanets, comets, qasars and other astronomical objects along the way. Needless to say, a lot of astronomers are very excited by this.

 

Now, some disclaimers: Gaia cannot map the entire Milky Way, due to being inside it - a lot of the galaxy actually blocks itself from view. Additionally, there are limits to the minimum brightness of stars that it can reliably track. In fact, it is expected that Gaia will map "only" around 1% of the entire contents of the galaxy. I say that in quotation marks, because that's still far more than any other single instrument has ever detected.

Not so, you cannot map a billion stars precisely (unless you redefine precision). You can only precisely map the current positions of objects whose velocity is similar to our sun, given space-time. You can map their position at a given distance (@distance/length of  light year)t years ago. But without the velocity and acceleration vector you cannot know where they are now, and even if you had these that now is irrelevant because no spatial-temperol reference frame exists in our visible universe.

All stars in the Milky Way galaxy are moving relative to one another, all stars in the milky way are accelerating relative to one another (even though they are in typically non-inertial reference frames, those reference frames themselves are in motion). You might be able to discern parallax and astronomical position over several years, but on the scale of local clusters, that precision declines greatly as distance increases. Lets say those distances are accurate to 1/1000000. If we use the equation (xk/4)^3 = y when y = 1 then then k = 4 and when y = 1,000,000,000 then xk/4 = 1000, then x = 4000 ly. Note there is no absolute way of knowing how inaccurate your distance measurement is.

At a error rate of 0.0001% the distance error is 1/250 of a light year or about 2.5 x 10^14 meters. If the distance error is   1/10,000 is 1/4th of a light years and 1/1000 (which I strongly suspect is the high end of their accuracy it is 2.5 ly. If we then consider a probable range it means stars have distance measurements of 2.5 to 25 ly in error at the minimum outside boundary of distance. the star field in not flat, and there is a preference against red stars at a distance so the reality is the error on the furthest stars in the billion is more like 100 ly in distance.

Ask yourself this question. How is it possible to know with precision the current position of a star at 1000s of ly from Sun whose velocity relative to our sun is different and constantly changing. So imagine you had a space ship and today, right now, you could go 0.1c to a star at a distance of 5000ly based on this precision (50000 years of travel).

Precision is this, if I have a high powered rifle and I mount it in a device where the barrel is firmly placed, and repeated clean and fire the weapon, the bullets every time hit the same target (barring hurricances, changes in gravity, and highly unexpected geological events). Its track per unit distance is precisely (key the word) the same, it never changes. But all my targets for a high powered rifle are the same, they coexist in a definable space-time relative to the rifles position. In long distances of space space-time reference frames are not easily defined because of things like dead stars,  black dwarves, black holes, and dark matter.

So as you travel to your d= 5000ly star you would miss the target by 10 - 100 ly (that would be 100 - 1000 more years of travel) because you got the velocity and arc of motion wrong. Over a period of 50000 years stars in our local cluster travel 3 or 4 light years and we know their positions 'precisely', but a star whose velocity and acceleration aren't know precisely would not be were we expected them to be. First, their original position changes by the time their light reaches earth, and then as we travel their position changes during the travel. 

It takes more than a few years of study by an orbital telescope to accurately measure distances and relative velocity, there are anomalies in between stars that alter our measurements (warping in space-time). Lets not feed their hype machine. It takes years of measuring stars and their motion to discern variations in velocity that reflect its space-time and the variation of space-time between the  object and the sun over time.
 

 

[Green Baron]

 

I remember, that for a palaeanthropological exhibition "Roots of Mankind", 2006 in Bonn, Germany, they built up a huge screen in the entryhall showing the movement of the brightest stars of the constellations over the last few hundred thousand years (i don't remember the exact number), to illustrate the timespan which the exhibition covered. Very impressive that was !

As i read the year ... that was of course the 150th of the Neandertal Neandertal :-)

 

Edited September 15, 2016 by Green Baron

[Streetwind]

Seven passionate paragraphs, @PB666, all to say what essentially boils down to "I disagree with your definition of one word, even though you've never given me your definition, so I just guessed that you defined it wrong so I can make myself appear knowledgeable". Bravo. Maybe if you keep trying, then one day, you too will be able to participate in a thread without coming across as a part of what makes the Science Forums such an incredibly frustrating place nowadays.

All of it completely past the point of the thread too, which is to acknowledge the incredible contribution to the field of astronomy that this instrument is currently making.

Some days I wonder why I keep coming back to this place.

Edited September 15, 2016 by Streetwind

[DerekL1963]

8 hours ago, Streetwind said:

This is actually a spacecraft/mission that I see almost never mentioned here on the forums for some reason... yet it has been quietly working away at its task

It's the whole "quietly working away"...  Science (real science, as opposed to movie, KSP, and Discovery Channel "science") is mostly boring and repetitive.  Boring and repetitive doesn't make the news.

That being said, this is very cool.

[RainDreamer]

 

And more videos about it are on ESA you tube channel, including an hour and a half long press conference video, if you are into that.

[Vanamonde]

Please don't complain about each other's posts. If you don't like it, don't read it. If somebody really bugs you, you can set that person to "ignore" and not even see his/her posts anymore. 

[PB666]

On 9/15/2016 at 0:35 PM, Streetwind said:

Seven passionate paragraphs, @PB666, all to say what essentially boils down to "I disagree with your definition of one word, even though you've never given me your definition, so I just guessed that you defined it wrong so I can make myself appear knowledgeable". Bravo. Maybe if you keep trying, then one day, you too will be able to participate in a thread without coming across as a part of what makes the Science Forums such an incredibly frustrating place nowadays.

All of it completely past the point of the thread too, which is to acknowledge the incredible contribution to the field of astronomy that this instrument is currently making.

Some days I wonder why I keep coming back to this place.

Where are their controls, by what absolute measure to they measure these distances. Since, in reality even our measurement of the Sun's gravity and mass is biased by an interpretation of G and each bodies gravitational constant, which may vary in cases up to 1/10^6 and may not be constant over the lifetime of the universe (in-fact probably is not constant over the life-time of the universe), because gravity is the warping caused by an amorphous collective quantum space-time, and space and time did not exist at the beginning of the universe, and probably did not resolved until the quantum singularity had 'fractured' in various and sundry way. Gravity as we know it probably evolved and is still evolving (e.g. potentially an influence of dark energy). The other name for dark matter is dark gravity, just to make a point, we have not isolated any particle that qualifies as dark matter.

I disagree that the word precision should be used out of a special context, yes. This is exactly the kind of scenario in science were 50 years on, after gathering more information about quantum mechanics and theory and experimentation concerning quantum space-time they come back and say well whoops we had to recondition the measurements back there with these new equations for estimating distances in space, particularly distances above and below the galactic plane.

[YNM]

TBH the billion star thing can be easily achieved without even having a distance limitation to MW's central blackhole. We just happen to have a bunch load of stars, and if Gaia can do it, brown dwarfs.

Also, the "precise" definition here is just the data as we have it, not all the perturbations and possible deviation. Who knows if the thing would explode as we reach them ?

@Streetwind : so you work for ESA ? Or is it some related institution ?

 

EDIT : Sorry mods, will remember that !

Edited September 20, 2016 by YNM

[Streetwind]

@YNM - I don't work for ESA, no. Though sometimes I wish I was I'm just a spaceflight and astronomy enthusiast who likes to follow the cool stuff that the various organizations are doing up there.

NASA missions are oftentimes well represented here on the forums, which isn't surprising, considering NASA still has as much budget as all other civilian spaceflight programs in the world combined. They're just by far the most involved and visible. Meanwhile, if there isn't some especially high-profile mission like Rosetta going on, you might almost think that the other organizations aren't even doing anything, what with the lack of talk about it. But that's far from the truth.

[YNM]

7 hours ago, Streetwind said:

... Meanwhile, if there isn't some especially high-profile mission like Rosetta going on, you might almost think that the other organizations aren't even doing anything, what with the lack of talk about it. But that's far from the truth.

Probably because missions to monitor a known thing (including earth observation satellites) are less fascinating to most people. Guess I'm included - TBH I know more of those missions to other worlds, such as Hayabusa2 or upcoming BepiColombo. Maybe I should start looking at those other ones !