APOD: The Local Fluff (2010 Aug 29)

[APOD Robot]

The Local Fluff

Explanation: The stars are not alone. In the disk of our Milky Way Galaxy about 10 percent of visible matter is in the form of gas, called the interstellar medium (ISM). The ISM is not uniform, and shows patchiness even near our Sun. It can be quite difficult to detect the local ISM because it is so tenuous and emits so little light. This mostly hydrogen gas, however, absorbs some very specific colors that can be detected in the light of the nearest stars. A working map of the local ISM within 10 light-years based on recent observations is shown above. These observations show that our Sun is moving through a Local Interstellar Cloud as this cloud flows outwards from the Scorpius-Centaurus Association star forming region. Our Sun may exit the Local Interstellar Cloud, also called the Local Fluff, during the next 10,000 years. Much remains unknown about the local ISM, including details of its distribution, its origin, and how it affects the Sun and the Earth.

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[Boomer12k]

I do not understand something.
In the picture, the sun is moving relatively down, away from the the galactic center.
On Dec,21, 2012 the sun is supposed to cross the galactic equator. And thus, Doomsday!
But, by the motion of the sun in this picture, it is down and away from that!
I just realized that it is a view from EARTH. Where the Sun crosses the galactic equator. Not out there. It is ONLY from our point of view!!!!
What makes people think it will have ANY EFFECT WHATSOEVER ON US?????

[bystander]

The Sun is moving to the left. The interstellar cloud is moving down. The picture doesn't show the Sun's movement with respect to the plane of the Galactic disk (equator). As for doomsday ... (I'm sure 21 Dec 2012 will be an event to rival Y2K)

[neufer]

The Local Fluff

http://antwrp.gsfc.nasa.gov/apod/ap020217.html

---

<<In recent millenia, the Sun has been passing through a Local Interstellar Cloud (LIC) that is flowing away from the Scorpius-Centaurus Association of young stars dominated by extremely hot and bright O and B spectral types, many of which will end their brief lives violently as supernovae. The LIC is itself surrounded by a larger, lower density cavity in the interstellar medium (ISM) called the Local Bubble, that was probably formed by one or more relatively recent supernova explosions.>>

As shown in a 2002 Astronomy Picture of the Day, located just outside the Local Bubble are: high-density molecular clouds such as the Aquila Rift which surrounds some star forming regions; the Gum Nebula, a region of hot ionized hydrogen gas which includes the Vela Supernova Remnant, which is expanding to create fragmented shells of material like the LIC; and the Orion Shell and Orion Association, which includes the Great Orion Nebula, the Trapezium of hot B- and O-type stars, the three belt stars of Orion, and local blue supergiant star Rigel.

Nearby (~200 parsecs) Geminga & Vela Pulsars in Gamma Ray Sky Credit : NASA/DOE/International LAT Team

---

<<Geminga is a neutron star 157 parsecs away in the constellation Gemini. Its name is both a contraction of "Gemini gamma-ray source", and gh'è minga "it's not there." The nature of Geminga was quite unknown for 20 years after its discovery by NASA's Small Astronomy Satellite (SAS-2). Finally, in 1991 the ROSAT satellite detected a periodicity of 0.237 seconds in soft x-ray emission. Thus, it is supposed that Geminga is a sort of neutron star: the decaying core of a massive star that exploded as a supernova about 300,000 years ago. This nearby explosion may be responsible for the low density of the interstellar medium in the immediate vicinity of the Solar System. This low-density area is known as the Local Bubble. Possible evidence for this includes findings by the Arecibo Observatory that local micrometre-sized interstellar meteor particles appear to originate from its direction.>>

[nstahl]

I'd expect the sun's velocity vector to be pretty much perpendicular to the radial vector to the center of the galaxy; it's not. I'm thinking it's a perspective problem due to the plane of the map not being the plane determined by those vectors, which would seem on the face of it to be the plane to use.

On further reflection maybe the obvious choice is the plane determined by the sun's velocity and the cloud's velocity. Those seem to be at right angles, which would be something of a coincidence surely.

Any idea how the plane was chosen? Comments?

[NobodyInParticular]

Other than the statistical likelihood of circularity, there's no reason to assume the sun's velocity is currently perpendicular to its galactic-center radial. Has that been measured?

[Henning Makholm]

On Dec,21, 2012 the sun is supposed to cross the galactic equator. And thus, Doomsday!

Supposed by whom? Certainly not by anyone with the least bit real knowledge of astronomy.

The IAU defines a "galactic coordinate system", according to which the galactic equatorial plane by definition passes through the Sun. In order for the Sun to cross the galactic plane, we first have to define a galactic plane that is independent of the Sun's motion. In theory we could just take the plane that passes through the galaxy's center of mass and is perpendicular to its total angular momentum. However, observational uncertainty severely limits the precision by which this theoretical plane can be determined in practice. To suppose that it is well-defined enough that the Sun can be said to pass through it at a particular date is thoroughly absurd.

I just realized that it is a view from EARTH. Where the Sun crosses the galactic equator. Not out there. It is ONLY from our point of view!!!!

Seen from Earth, the Sun crosses the galactic equator twice a year. A Doomsday-causing effect is almost certainly ruled out by the empirical fact that Doomsday failed to happen the last several tens of times such a crossing happened.

[neufer]

Other than the statistical likelihood of circularity, there's no reason to assume the sun's velocity is currently perpendicular to its galactic-center radial. Has that been measured?

On average:

1) the stars in our stellar neighborhood should be moving perpendicular to the galactic-center radial
2) and the sun is moving just ~20 km/s relative to them

so the earth is moving within 5º of the perpendicular to the galactic-center radial

http://en.wikipedia.org/wiki/Sun

[Boomer12k]

On Dec,21, 2012 the sun is supposed to cross the galactic equator. And thus, Doomsday!

Supposed by whom? Certainly not by anyone with the least bit real knowledge of astronomy.

The IAU defines a "galactic coordinate system", according to which the galactic equatorial plane by definition passes through the Sun. In order for the Sun to cross the galactic plane, we first have to define a galactic plane that is independent of the Sun's motion. In theory we could just take the plane that passes through the galaxy's center of mass and is perpendicular to its total angular momentum. However, observational uncertainty severely limits the precision by which this theoretical plane can be determined in practice. To suppose that it is well-defined enough that the Sun can be said to pass through it at a particular date is thoroughly absurd.

I just realized that it is a view from EARTH. Where the Sun crosses the galactic equator. Not out there. It is ONLY from our point of view!!!!

Seen from Earth, the Sun crosses the galactic equator twice a year. A Doomsday-causing effect is almost certainly ruled out by the empirical fact that Doomsday failed to happen the last several tens of times such a crossing happened.

Look up 2012, Mayan doomsday prophecy. This is supposed to be when the Sun goes back up across the galactic plane. It is all over the history channel shows.

[Henning Makholm]

On average:

1) the stars in our stellar neighborhood should be moving perpendicular to the galactic-center radial
2) and the sun is moving just ~20 km/s relative to them

so the earth is moving within 5º of the perpendicular to the galactic-center radial

http://en.wikipedia.org/wiki/Sun

However, the Wikipedia article says: The general direction of the Sun's galactic motion is towards the star Vega in the constellation of Lyra at an angle of roughly 60 sky degrees to the direction of the Galactic Center.

[Edit: Closer following of Wikipedia links imply that the 60° movement is relative to the common motion of the nearby stars, which is indeed perpendicular to the galactic radial. So there is no conflict after all.]

I'm not sure that your point (1) should be assumed to hold. One can imagine that passage in and out of the spiral arms give rise to a systematic variation in radial velocity that the stars in our neighborhood would all share.

[Henning Makholm]

Look up 2012, Mayan doomsday prophecy. This is supposed to be when the Sun goes back up across the galactic plane. It is all over the history channel shows.

Again, who does that supposing? Wild-eyed crackpots, mostly. Followed by a flock of media people who don't care whether what they say is true or false as long as it draws in an audience.

[Chris Peterson]

Look up 2012, Mayan doomsday prophecy. This is supposed to be when the Sun goes back up across the galactic plane. It is all over the history channel shows.

And it's wrong. The Sun is not crossing the galactic plane in 2012. The Sun does bob up and down across what might be considered the galactic plane, however. But it does this over hundreds of millions of years, and any actual physical plane is so undefined that we spend hundreds of thousands of years about it- certainly not one day!

People who buy into the Mayan nonsense also tend to confuse non-physical alignments, such as when the galactic center crosses the ecliptic, with "crossing the galactic plane". And then there is the little problem that there is no Mayan doomsday prophecy, and nothing in Mayan mysticism suggested that the world would end in 2012. But the world is now full of people with seriously poor thinking skills.

[Chris Peterson]

Other than the statistical likelihood of circularity, there's no reason to assume the sun's velocity is currently perpendicular to its galactic-center radial. Has that been measured?

Yes, the Sun's velocity is known in terms of galactic coordinates. And like essentially every star in the galactic disc, its orbit is substantially circular and lies approximately parallel to the galactic plane.

[Ann]

Look up 2012, Mayan doomsday prophecy. This is supposed to be when the Sun goes back up across the galactic plane. It is all over the history channel shows.

And it's wrong. The Sun is not crossing the galactic plane in 2012. The Sun does bob up and down across what might be considered the galactic plane, however. But it does this over hundreds of millions of years, and any actual physical plane is so undefined that we spend hundreds of thousands of years about it- certainly not one day!

People who buy into the Mayan nonsense also tend to confuse non-physical alignments, such as when the galactic center crosses the ecliptic, with "crossing the galactic plane". And then there is the little problem that there is no Mayan doomsday prophecy, and nothing in Mayan mysticism suggested that the world would end in 2012. But the world is now full of people with seriously poor thinking skills.

Like Chris points out, a crossing of the galactic plane takes thousands of years, so it is next to impossible to say when exactly the true crossing takes place. Of course we have no reason whatsoever to believe that anything in particular will happen just because we cross the galactic plane.

But in any case, we are not even close to crossing the galactic plane. We clearly see more of the galactic bulge "below" the galactic plane in Sagittarius than we do "above" the galactic plane in upper Scorpius.

This is what the Milky Way looks like from our perspective:



If we were close to crossing the galactic plane of the Milky Way, then the dust lane of our galaxy would seem to cut the galactic bulge exactly in the middle, just the way it does (from our perspective) in NGC 891:



Nothing is going to happen when we cross the galactic plane, but the question is moot anyway, since we aren't going to cross the galactic plane in 2012.

Ann

[orin stepanek]

I wonder where ideas like 2012 doomsday come from? it's as bad as 'all the computers are going to crash at the end of the 20th century'. They didn't crash and we can't predict doomsday either.

[celestemekent]

Is there some reason why we dont call all that fluff what it really is, Plasma, the 5th state of matter. Anytime there is movement within such an electrified cloud there will be an electrical current.

[Chris Peterson]

I wonder where ideas like 2012 doomsday come from? :roll: it's as bad as 'all the computers are going to crash at the end of the 20th century'. They didn't crash and we can't predict doomsday either.

There was rational reason to be worried about computers crashing at the end of the 20th century. That they didn't was some combination of miscalculation, careful preparation, and luck. But there is no rational reason at all to think that doomsday will come in 2012. The funny thing is, even the Mayans didn't think that! It's just the New Age kooks misunderstanding the Mayan calendar.

[Chris Peterson]

Is there some reason why we dont call all that fluff what it really is, Plasma, the 5th state of matter. Anytime there is movement within such an electrified cloud there will be an electrical current.

What we call it technically is "the interstellar medium", and it consists of both neutral and ionized gases, as well as dust. So it isn't a plasma, although it contains matter in a plasma state. (Plasma is not the "5th state of matter", but merely one of many loosely defined states, in this case a gas containing some ionized atoms.)

Of course, if plasma moves, you also have a movement of charge, which might be considered an electrical current. But the term is generally reserved for the directed movement of electrons under the influence of a field, and such currents need not occur in a moving plasma. In fact, the ISM is so extremely rarefied that any electric currents are almost certainly very tiny, and very disordered as well. Over galactic scales, the ISM is responsible for maintaining a small magnetic field, but over any sort of local scale (as between stars) both electrical and magnetic densities are very small.

[neufer]

-----------------------
ISM is an acronym of:

* Imperial Service Medal
* Incorporated Society of Musicians
* Indian School of Mines
* Industrial, Scientific and Medical - ISM band radio frequencies
. allocated for industrial, scientific and medical processes.
* Institute for Supply Management
* International School of Management
* International Safety Management-Code
* The International Spy Museum in Washington, D.C.
* International Socialist Movement - Scotland
* International Society for Micropiles
* International Solidarity Movement - Palestinian
* International Sports Management Limited
* Interstellar medium
* InterSystems MUMPS
* Italian Social Movement
------------------------------

From Ancient Greek -ισμός (-ismos), a suffix that forms abstract nouns of action, state, condition, doctrine; from Ancient Greek -ισμα (-isma), from stem of verbs in -ιζειν (-izein). Many words are likely to be derived from the French -isme, which in turn are derived from the Latin -ismus. Other words are created newly in English, French or Latin with the suffix of that language.

Suffix -ism

1. the action or result of a verb

baptism (from baptise)

2. a principle, belief or movement

chauvinism (coined after Nicolas Chauvin)
conservatism (from conservative)
Cubism
externalism
feminism (from femina, Latin for woman)
liberalism
Marxism (coined after Karl Marx)

3. a form of prejudice or discrimination, either for or against a group

alphabetism (from alphabet)
nationism (from nation)
racism (from race)
sexism (from sex)
sexualism (from sexuality)

4. the defining attribute of a person or thing

heroism (from hero)

5. a disorder

autism (from autós, Greek for "self")

[orin stepanek]

I wonder where ideas like 2012 doomsday come from? it's as bad as 'all the computers are going to crash at the end of the 20th century'. They didn't crash and we can't predict doomsday either.

There was rational reason to be worried about computers crashing at the end of the 20th century. That they didn't was some combination of miscalculation, careful preparation, and luck. But there is no rational reason at all to think that doomsday will come in 2012. The funny thing is, even the Mayans didn't think that! It's just the New Age kooks misunderstanding the Mayan calendar.

You may be right Chris; but I never did buy into the millennium computer scare. I figured it would pass; and it did. So maybe I was just lucky. Any way; I get tired of hearing about all the doomsday and end of world prophesies.

[neufer]

Is there some reason why we dont call all that fluff what it really is, Plasma, the 5th state of matter.

"Local Fluff" contains a wispy mixture of hydrogen and helium atoms at a temperature of ~6000 K.

Hence, these atoms have a thermal energy kT of ~ 0.5 eV. [k ~ (1 eV/12,000 K)]

It takes 13.6 eV (~ 27 kT) to ionize a hydrogen atom (and much more to ionize helium).

Anytime there is movement within such an electrified cloud there will be an electrical current.

Plasmas are electrically neutral overall.

However, movement through a magnetic field will induce currents.

[Sam]

I have trouble comprehending how the ISM can have such low density yet still have such a high temperature. The same thing is true of the Earth's thermosphere: very hot, but would be "felt" as very cold because it's so rarefied. Wouldn't the heat of an isolated hydrogen atom radiate away very quickly into empty space if there are no other atoms nearby to insulate it? What would the "temperature" be of the empty part of the cubic centimeter, the part that does not have an atom in it?

_________
Sam Rudy

[neufer]

I have trouble comprehending how the ISM can have such low density yet still have such a high temperature. The same thing is true of the Earth's thermosphere: very hot, but would be "felt" as very cold because it's so rarefied. Wouldn't the heat of an isolated hydrogen atom radiate away very quickly into empty space if there are no other atoms nearby to insulate it?

The temperature of these ground state hydrogen atoms is defined by their random velocities (~5 km/s). They lack a mechanism to radiate even if they collided with one another at their mild energies of a half an electron volt (which is highly unlikely in any event).

Black bodies radiate away their energy but transparent bodies DO NOT.

Even the earth's troposphere is full of gases that are highly transparent in both the visible and the infrared (e.g., nitrogen, oxygen, & argon). The troposphere can thermally radiate ONLY through the intermediary of trace greenhouse gases like carbon dioxide, water and methane.

What would the "temperature" be of the empty part of the cubic centimeter, the part that does not have an atom in it?

What would it's color be? What would it's smell be? What would it's taste be?[

What is the sound of no hands clapping?

[ajeadie18]

There are billion of stars; we only have one in our Solar System: the name of our star is Sun - surely it deserves an uppercase "S"?

ajeadie18

[Beyond]

There are billion of stars; we only have one in our Solar System: the name of our star is Sun - surely it deserves an uppercase "S"?

ajeadie18

I thought the name of OUR star was SOL.