APOD: M81 versus M82 (2013 Sep 25)

[Nitpicker]

Neufer, that diagram of concentric, twisted ellipses is also very informative, thanks. And hats off to C.C. Lin and Frank Shu.

[Nitpicker]

I should point out that M81 is 12 Mly away such that 0.1 arcsec ~ 6 lyr.

Therefore Adriaan van Maanen was "observing"
relativistic orbital proper motions ...

In other words, it is only the length of the cyan-coloured arrows that is related to the cyan-coloured scale bar. M81 itself appears much larger to us: ~800-900 arcsec across.

(Actually, it doesn't appear to me at all, because I am too far South to see much of anything North of 50 degrees Declination.)

[Nitpicker]

Ann, thanks for the link to that CFA article. It has left me thinking that it really is too complicated to try and describe in a few sentences. From now on, I resolve to refrain from such attempts.

I have a (distant) background in computational fluid dynamics, and one of the difficulties encountered in that field, is relating the mathematics of partial differential equations, to the results obtained when solving them numerically. One often ends up waving one's arms around and saying "ooh, look at that pretty thing!". I feel the same might be said of these mind-bogglingly complex gravitational models of galaxies (at least as far as my feeble mind is concerned).

[neufer]

I should point out that M81 is 12 Mly away such that 0.1 arcsec ~ 6 lyr.

Therefore Adriaan van Maanen was "observing"
relativistic orbital proper motions ...

In other words, it is only the length of the cyan-coloured arrows that is related to the cyan-coloured scale bar.
M81 itself appears much larger to us: ~800-900 arcsec across.

The cyan-coloured scale bar is a velocity measure of 0.1 arcsec PER ANNUM.

God only knows what Adriaan van Maanen was actually "observing"
but it was a neat diagram and the conversation was starting to drift off.

[Nitpicker]

At a guess, it is perhaps "Annual Proper Motion in arc seconds" as measured from the centre of M81, not as measured from our sky.

I've never heard of Proper Motion being relative to anything other than the Solar System, but things may have been different in 1921.

[Nitpicker]

But don't believe me (really don't, I speculate far too much), this article would seem to be more enlightening:

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

[deathfleer]

[size=125][b][color=#0000FF]Plate IV in Adriaan van Maanen's 1921 paper (MA21) showing astrometrically measured internal motions for M81. '[i]The arrows indicate the mean annual motions.[/i]'[/color][/b][/size]

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Am I not right if I say
that the M81 's core is spinning anti clockwise?

• You are indeed not right ...

<<For the most part, spiral galaxies have trailing arms. All grand design spiral arms are trailing. Statistically, the vast majority most spiral galaxies have trailing arms. The source of leading-edge arms is believed to be the result from collisions causing retrograde perturbations. It's also been observed that only parts of the galaxy may be affected, i.e outer arms may be leading while the inner arms are trailing. NGC 4622 is an example, and possibly M81.>>

I should point out that M81 is 12 Mly away such that 0.1 arcsec ~ 6 lyr.

[c]Therefore Adriaan van Maanen was "observing"
relativistic orbital proper motions ... [/c]

Thanks Mr Neufer. That (last) diagram is a beautiful answer.

[neufer]

At a guess, it is perhaps "Annual Proper Motion in arc seconds" as measured from the centre of M81, not as measured from our sky.

A tenth of an arc second is a 13 millionth of 360º
so that would mean galactic orbits taking ~ 26 million years.

That is STILL way too fast by an order of magnitude!

(However, Adriaan van Maanen was, in fact, "measuring" proper motions as best he could from a hundred times further away and got motions that were too fast by three orders of magnitude.)

I've never heard of Proper Motion being relative to anything other than the Solar System, but things may have been different in 1921.

Things were indeed different a hundred years ago... astrometric measurements were much cruder.

The upcoming Gaia space observatory represents the first time humans will be able to observe proper motions BEYOND our own galaxy:

<<Gaia is a space observatory to be launched by the European Space Agency (ESA) in November 2013. The mission aims to compile a 3D space catalogue of approximately 1 billion stars, or roughly 1% of stars in the Milky Way. Successor to the Hipparcos mission, it is part of ESA's Horizon 2000 Plus long-term scientific program. Gaia will monitor each of its target stars about 70 times to a magnitude 20 over a period of 5 years. Gaia will create an extremely precise three-dimensional map of stars throughout our Milky Way galaxy and beyond, determining the positions, distances, and annual proper motions of 1 billion stars with an accuracy of about 20 µas (microarcsecond) at 15 mag, and 200 µas at 20 mag.>>

[Nitpicker]

Yes, after I read the story of van Maanen linked in my last , it dawned on me that my guess was a bad one.

I shall go and sit in the corner for a few days.

[neufer]

Yes, after I read the story of van Maanen linked in my last , it dawned on me that my guess was a bad one.

I shall go and sit in the corner for a few days.

<<"Jack" Horner (born June 15, 1946) is an American paleontologist who discovered and named Maiasaura, or "Good Mother Lizard", providing the first clear evidence that some dinosaurs cared for their young. He is one of the best-known paleontologists in the United States. In addition to his many paleontological discoveries, Horner served as the technical advisor for all of the Jurassic Park films, and even served as partial inspiration for one of the lead characters, Dr. Alan Grant.

Horner's 2009 book, How to Build a Dinosaur: Extinction Doesn't Have to Be Forever, describes his plan to recreate a dinosaur by genetically "nudging" the DNA of a chicken. In 2003, he discovered a fossilized tyrannosaur leg bone from which paleontologist Mary Higby Schweitzer was able to retrieve proteins in 2007. As of 2011 Horner is pursuing the project to develop the animal, which he describes as a "chickenosaurus", with a team of geneticists.>>

[neufer]

[b][color=#0000FF]Before and after photos of the galaxy M81 showing the appearance of a brand new 11.7 magnitude supernova. The object is located in the galaxy’s plane 54″ west and 21″ south of its center. Credit: E. Guido, N. Howes, M. Nicolini[/color][/b]

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Bright New Supernova Blows Up
in Nearby M82, the Cigar Galaxy
by Bob King, Universe Today, Jan. 22, 2014

<<Wow! Now here’s a supernova bright enough for even small telescope observers to see. And it’s in a bright galaxy in Ursa Major well placed for viewing during evening hours in the northern hemisphere. Doesn’t get much better than that! The new object was discovered last night by S.J. Fossey; news of the outburst first appeared on the Central Bureau for Astronomical Telegrams “Transient Objects Confirmation Page”

Astronomers are saying this new supernova is currently at magnitude +11 to +12, so its definitely not visible with the naked eye. You’ll need a 4 inch telescope at least to be able to see it. It’s amazing it wasn’t found sooner (update — see below, as perhaps it was!). M82 is a popular target for beginning and amateur astronomers; pre-discovery observations show it had already brightened to magnitude 13.9 on the 16th, 13.3 on the 17th and 12.2 on the 19th. Cold winter weather and clouds to blame?

UPDATE: Fraser and team from the Virtual Star Party actually imaged M82 on Sunday evening, and you can see it in the video below at the 22 minute mark. It really looks like a bright spot is showing up — and that’s about a day before it was announced. Did they catch it? In the video the galaxy appears upside down as compared to the images here:

Click to play embedded YouTube video.

>>