APOD: The Galactic Center in Infrared (2016 Jan 17)

[APOD Robot]

The Galactic Center in Infrared

Explanation: The center of our Galaxy is a busy place. In visible light, much of the Galactic Center is obscured by opaque dust. In infrared light, however, dust glows more and obscures less, allowing nearly one million stars to be recorded in the featured photograph. The Galactic Center itself appears on the left and is located about 30,000 light years away towards the constellation of the Archer (Sagittarius). The Galactic Plane of our Milky Way Galaxy, the plane in which the Sun orbits, is identifiable by the dark diagonal dust lane. The absorbing dust grains are created in the atmospheres of cool red-giant stars and grow in molecular clouds. The region directly surrounding the Galactic Center glows brightly in radio and high-energy radiation, and is thought to house a large black hole.

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[Ann]

Interesting! It is always interesting to see infrared "revelations" of objects that are hidden from view in visible light.

Click to view full size image

Central parts of the Milky Way. Mosaic: ESO/VVV Consortium

There are so many different ways to peer through the dust of our galaxy, and there are many fascinating infrared views available.

One of my favorites is the one at left, from ESO, constructed from large numbers of infrared images of our galaxy taken by the VISTA Telescope at ESO’s Paranal Observatory in Chile. What I like about it is that it is so delicately transparent, and you can see fascinating details in the dust lanes. For example, there appears to be some major star formation going on in a couple of dust lanes at far right, or at least there seems to be several large collections of young stars in that vicinity.

There are also fantastic closeups of the innermost few hundred parsecs or so of our own galaxy, but that is another kettle of fish. I think this one is my favorite.

Ann

[heehaw]

The American Astronomical Society met in Toronto, Canada, in August 1959, when I was 19 and already an astronomer. At the meeting, Ambartsumian suggested the presence of a blackhole at the center of our Galaxy, and I thought that was the stupidest idea I'd ever heard in my life!

[Boomer12k]

The American Astronomical Society met in Toronto, Canada, in August 1959, when I was 19 and already an astronomer. At the meeting, Ambartsumian suggested the presence of a blackhole at the center of our Galaxy, and I thought that was the stupidest idea I'd ever heard in my life!

They laughed in the early 70's when I said there were other planets around stars... I hope you were not one of those who laughed. But don't feel bad... Fred Hoyle STILL does not accept the Expanding Universe.
So we are all in good company...

They nearly KILLED Galileo...


:---[===] *

[Glima49]

The American Astronomical Society met in Toronto, Canada, in August 1959, when I was 19 and already an astronomer. At the meeting, Ambartsumian suggested the presence of a blackhole at the center of our Galaxy, and I thought that was the stupidest idea I'd ever heard in my life!

And indeed it does: one with about 4 million times the mass of the sun. About 350 years ago the nucleus was active as far as I know. I wonder when will it experience activity again? It's a shame 'G2' was a bust.

[Chris Peterson]

The American Astronomical Society met in Toronto, Canada, in August 1959, when I was 19 and already an astronomer. At the meeting, Ambartsumian suggested the presence of a blackhole at the center of our Galaxy, and I thought that was the stupidest idea I'd ever heard in my life!

Perhaps you were the better scientist! I guess it depends upon the strength of the evidence that was presented. Certainly, science depends upon a high level of skepticism and a refusal to accept radical new ideas until they are well supported by evidence. Sometimes scientists get things right by accident. That isn't the mark of good science.

The important distinction between science and most other mechanisms people use to acquire knowledge is that it always trends towards a more accurate understanding of nature. It allows understanding to change as required to match observation.

[neufer]

Fred Hoyle STILL does not accept the Expanding Universe.

Fred Hoyle died in 2001 never accepting the Big Bang theory.

However, his whole steady state cosmology theory was based upon an Expanding Universe.

<<Hoyle offered an explanation for the appearance of new matter by postulating the existence of what he dubbed the "creation field", or just the "C-field", which had negative pressure in order to be consistent with the conservation of energy and drive the expansion of the universe. These features of the C-field anticipated the later development of cosmic inflation.>>

[neufer]

The American Astronomical Society met in Toronto, Canada, in August 1959, when I was 19 and already an astronomer. At the meeting, Ambartsumian suggested the presence of a blackhole at the center of our Galaxy, and I thought that was the stupidest idea I'd ever heard in my life!

Perhaps you were the better scientist! I guess it depends upon the strength of the evidence that was presented. Certainly, science depends upon a high level of skepticism and a refusal to accept radical new ideas until they are well supported by evidence.

Sometimes scientists get things right by accident. That isn't the mark of good science.

• That's the stupidest idea I'd ever heard in my life!

[Ann]

Fred Hoyle STILL does not accept the Expanding Universe.

Fred Hoyle died in 2001 never accepting the Big Bang theory.

However, his whole steady state cosmology theory was based upon an Expanding Universe.

<<Hoyle offered an explanation for the appearance of new matter by postulating the existence of what he dubbed the "creation field", or just the "C-field", which had negative pressure in order to be consistent with the conservation of energy and drive the expansion of the universe. These features of the C-field anticipated the later development of cosmic inflation.>>

What was wrong about Fred Hoyle's Steady State hypothesis was that it postulated that the universe is eternal and unchanging, apart from the fact that it is expanding. I think, for example, that Hoyle believed that the overall density of the universe always remains the same.

We now know, of course, that the universe has changed tremendously since its infancy.

Ann

[Chris Peterson]

Sometimes scientists get things right by accident. That isn't the mark of good science.

• That's the stupidest idea I'd ever heard in my life!

Patently false given that you've heard the idea that Shakespeare wasn't the author of Shakespeare!

[neufer]

---

Sometimes scientists get things right by accident. That isn't the mark of good science.

That's the stupidest idea I've ever heard in my life!

Patently false given that you've heard the idea that Shakespeare wasn't the author of Shakespeare!

1) The Scientific method STARTS with hypotheses (right or wrong) that are compatible with all well established observations.

2) The Scientific method CONTINUES by testing those hypotheses
and then refining, altering, expanding or rejecting those hypotheses.

Thinking that one is smart enough to reject some hypothesis out of hand simply because it is TOO crazy {rather than because it is in clear disagreement with well established observations) is nEVER good science.

"We are all agreed that your theory is crazy. The question which divides us is whether it is crazy enough to have a chance of being correct. My own feeling is that it is not crazy enough."

- Said to Wolfgang Pauli after his presentation of Heisenberg's and Pauli's nonlinear field theory of elementary particles, at Columbia University (1958), as reported by F. J. Dyson in his paper “Innovation in Physics”.

What was wrong about Fred Hoyle's Steady State hypothesis was that it postulated that the universe is eternal and unchanging, apart from the fact that it is expanding.

What was wrong about Fred Hoyle's Steady State hypothesis was that it didn't (and couldn't) predict:

• 1) Cosmic microwave background radiation (including detailed structure).
  
  2) Abundances of helium-4, helium-3, deuterium, and lithium-7 as ratios to the amount of ordinary hydrogen.
  
  3) Detailed observations of the morphology and distribution of galaxies and quasars.
  
  4) Cosmic acceleration.

[Chris Peterson]

1) The Scientific method STARTS with hypotheses (right or wrong) that are compatible with all well established observations.

Yes, but that doesn't mean that the formation of a hypothesis is good science. Frequently, it is inspiration, and while that is essential, it isn't scientific and it is wrong far more often than it's right. So when somebody proposes a bold new idea (that ultimately turns out to be correct), that proposition isn't necessarily good science, or even science at all.

(And I'd argue that the scientific method starts with making an observation, not making a hypothesis.)

2) The Scientific method CONTINUES by testing those hypotheses
and then refining, altering, expanding or rejecting those hypotheses.

Which is where we see actual science occur.

Thinking that one is smart enough to reject some hypothesis out of hand simply because it is TOO crazy {rather than because it is in clear disagreement with well established observations) is nEVER good science.

Rejecting isn't the same as not accepting. In fact, not initially accepting such a hypothesis is at the core of good science.

[neufer]

1) The Scientific method STARTS with hypotheses (right or wrong) that are compatible with all well established observations.

Yes, but that doesn't mean that the formation of a hypothesis is good science. Frequently, it is inspiration, and while that is essential, it isn't scientific and it is wrong far more often than it's right. So when somebody proposes a bold new idea (that ultimately turns out to be correct), that proposition isn't necessarily good science, or even science at all.

(And I'd argue that the scientific method starts with making an observation, not making a hypothesis.)

The Scientific method STARTS with hypotheses (right or wrong) that are compatible with all well established observations...and which are often (but not always) stimulated by some new (though less well established) observations.

<<It was in the early 1950s when Prof. Victor Ambartsumian (18 September 1908 – 12 August 1996) first raised the issue of the Activity of Nuclei of Galaxies (AGN). In his famous report at the Solvay Conference on Physics (Brussels, 1958) Ambartsumian said that enormous explosions take place in galactic nuclei and as a result a huge amount of mass is expelled. In addition, if this was so, these galactic nuclei must contain bodies of a huge mass and unknown nature. During a break in the session Walter Baade went up to Ambartsumian and said, "Professor Ambartsumian, you have come from the Soviet Union, and I from America. Logically speaking, you should be a materialist, and I an idealist. But what you have just said is nothing other than a pure idealism! It’s fantastic! You speak about some kind of 'non-stellar' objects which no one has seen. So it must be something inexplicable, mysterious."

The idea about the activity of galactic nuclei at first was accepted skeptically and only after many years, under the pressure of observations (the discovery of quasars, radio outbursts of galaxies, consequences of explosions in nuclei, ejection from nuclei, etc.) did it gain recognition. The concept of AGN now is widely accepted.

Ten years after the Solvay conference, at the plenary session of the IAU in Prague, the well-known American astronomer Alan Sandage said, “today, no astronomer would deny the mystery surrounding the nuclei of galaxies or that the first to recognize the rich reward held in this treasury was Viktor Ambartsumian.” As Victor Ambartsumian himself noted, the concept of active galactic nuclei occupies a special place among his scientific ideas. It was proposed by Ambartsumian more than half a century ago and was recognized by the U.S. National Academy of Sciences as revolutionary, on a copernican scale.>>

[Chris Peterson]

(And I'd argue that the scientific method starts with making an observation, not making a hypothesis.)

The Scientific method STARTS with hypotheses (right or wrong) that are compatible with all well established observations[/size]...and which are often (but not always) stimulated by some new (though less well established) observations.

Suit yourself. There is no THE scientific method. I always teach my students that scientific thinking begins with an observation that suggests a question. That makes much more sense to them than the idea that it somehow starts with a hypothesis, and also makes it much easier for them to apply.

[starsurfer]

The Galactic Center itself appears on the left and is located about 30,000 light years away towards the constellation of the Archer (Sagittarius).

I thought the centre of the Milky Way was 26,000 light years from Earth?

[starsurfer]

The American Astronomical Society met in Toronto, Canada, in August 1959, when I was 19 and already an astronomer. At the meeting, Ambartsumian suggested the presence of a blackhole at the center of our Galaxy, and I thought that was the stupidest idea I'd ever heard in my life!

They laughed in the early 70's when I said there were other planets around stars... I hope you were not one of those who laughed. But don't feel bad... Fred Hoyle STILL does not accept the Expanding Universe.
So we are all in good company...

They nearly KILLED Galileo...


:---[===] *

Don't forget Nicolaus Copernicus as well. Truth is often stranger than fiction.

[Chris Peterson]

The Galactic Center itself appears on the left and is located about 30,000 light years away towards the constellation of the Archer (Sagittarius).

I thought the centre of the Milky Way was 26,000 light years from Earth?

When it comes to astronomical distances, 26,000 ly is probably well described as "about 30,000 ly", given that the likely uncertainty is greater than the difference. Or was when this APOD first ran. Actual estimates range from less than 24,000 to nearly 29,000, and may change yet again if we figure out better ways of determining this hard to measure value.

[Jim Leff]

I hope this isn't too much of a tangent, but all the talk of dust made me think about how unbelievably sparse even "thick" interstellar dust is.

Per this link in today's APOD, the most abundant interstellar molecule is H2. So I wonder whether even at this extreme sparseness, if a spacecraft going extremely fast - perhaps 50k-100k mph - might gather and use enough H2 to significantly boost its velocity? Or is it still a trivial amount even at those speeds (or an order of magnitude higher)?

[Chris Peterson]

I hope this isn't too much of a tangent, but all the talk of dust made me think about how unbelievably sparse even "thick" interstellar dust is.

Per this link in today's APOD, the most abundant interstellar molecule is H2. So I wonder whether even at this extreme sparseness, if a spacecraft going extremely fast - perhaps 50k-100k mph - might gather and use enough H2 to significantly boost its velocity? Or is it still a trivial amount even at those speeds (or an order of magnitude higher)?

I think it's still uncertain if a Bussard ramjet or similar system could work in most interstellar space, where the ISM is very tenuous. It almost certainly could work in regions where the gas density is higher.

[Jim Leff]

scientific thinking begins with an observation that suggests a question. That makes much more sense to them than the idea that it somehow starts with a hypothesis, and also makes it much easier for them to apply.

That's a distinction without a difference. Even if a hypothesis seemingly springs from deep within the recesses of a person's mind/imagination/intuition, it always stems from observation of some sort at some level. There is no such thing as a purely hermetic hypothesis.

[Jim Leff]

I think it's still uncertain if a Bussard ramjet or similar system could work in most interstellar space, where the ISM is very tenuous. It almost certainly could work in regions where the gas density is higher.

Oh, I wouldn't imagine that current ramjet tech would apply. Just wondering what the total volume of H2 scooped up at such speeds (from a reasonably-sized "scoop".... say <1km in width) might be....in typical space. To compute it from higher density areas would be cheating - I'd think it unlikely that most flight plans could include significant travel through such areas.

[neufer]

(And I'd argue that the scientific method starts with making an observation, not making a hypothesis.)

The Scientific method STARTS with hypotheses (right or wrong) that are compatible with all well established observations...and which are often (but not always) stimulated by some new (though less well established) observations.

Suit yourself. There is no THE scientific method. I always teach my students that scientific thinking begins with an observation that suggests a question. That makes much more sense to them than the idea that it somehow starts with a hypothesis, and also makes it much easier for them to apply.

The important point is that BOTH observations & the making of (often crazy seeming) hypotheses are vitally important for science.

Hypotheses should be dismissed out of hand ONLY if they are INcompatible with well established observations, IMO.

(It is certainly permissible, however, for hypotheses to be dismissed by experimental scientists if they are untestable.)

[Chris Peterson]

I think it's still uncertain if a Bussard ramjet or similar system could work in most interstellar space, where the ISM is very tenuous. It almost certainly could work in regions where the gas density is higher.

Oh, I wouldn't imagine that current ramjet tech would apply. Just wondering what the total volume of H2 scooped up at such speeds (from a reasonably-sized "scoop".... say <1km in width) might be....in typical space. To compute it from higher density areas would be cheating - I'd think it unlikely that most flight plans could include significant travel through such areas.

There are actually a few papers on the subject of Bussard ramjets (which aren't current technology, of course) that consider how big the scoops would need to be, how much power would be required to sustain them, and how much thrust could be produced given different assumptions about ISM density and different possible fusion reactions.

[Jim Leff]

PS - I'd imagine there'd be some serious inefficiency involved in transferring errant H2 molecules from the "scoop" and into actual use...

[neufer]

scientific thinking begins with an observation that suggests a question. That makes much more sense to them than the idea that it somehow starts with a hypothesis, and also makes it much easier for them to apply.

That's a distinction without a difference. Even if a hypothesis seemingly springs from deep within the recesses of a person's mind/imagination/intuition, it always stems from observation of some sort at some level. There is no such thing as a purely hermetic hypothesis.

There are hermetically sealed Gedankenexperiments; e.g., Schrödinger's cat, Einstein's spaceship or elevator.