Author Topic: Saturday 30th April - Minkowski’s Object  (Read 6003 times)

Lightbulb500

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Saturday 30th April - Minkowski’s Object
« on: April 30, 2011, 03:57:45 pm »
Today's OOTD is a team effort by myself and Stellar190 and it focuses on a small clump of gas also known as Minkowski’s Object (ARP 133)

Minkowski’s Object in Visible Light Credit: SDSS

The object was first identified as 'interesting' in 1958 by Rudolph Minkowski1.
It sits 'just' outside the large Elliptical galaxy NGC 0541 which has at some time in the recent past had a close encounter with the interacting galaxies NGC 0545 and NGC 0547, shown by the 'star stream' that trails off in their direction. The group lies within the cluster Abell 0194 which is located around 300 million light years from us here on Earth.



The main HI region of Minkowski’s Object weighs in at around 4.9 x 10^8 solar masses - about 0.07% the mass of the Milky Way.

The Stellar bridge measures approximately 20 x 45 Kpc and contains around 3x10^9 solar masses of material - in comparison the Milky Way contains around 7.0×10^11 solar masses of material - meaning that the Milky Way contains roughly 233 times more material than the bridge.

At first Minkowski’s Object was considered to be an irregular galaxy that simply got in the way of a radio jet, causing the subsequent starburst documented in quite a few papers since the object’s discovery in 1958, but a paper in 2006 by Croft et al Suggests something quite different:

Minkowski’s Object used to be part of the Intergalactic medium surrounding NGC 0541, the intergalactic medium is mostly composed of ionized hydrogen and lurks between galaxies; it’s the stuff that causes ‘Extinction’, which is when the light from galaxies is absorbed by the material in between us and the light source.
Anyway, our cloud of gas was slightly warmer and denser than the surrounding areas, and happened to be in the path of a jet of radio waves coming from the core of NGC 0541. The jet ploughed straight through the cloud, shoving it out of the way and cooled the gas, causing it to collapse into molecular clouds and set off a huge starburst that churned out 1.9 x 10^6 solar masses of stars 7.5 million years ago.

To back this up, there appears to be no older stellar populations in the object, the only stars Croft et al can find are blue supergiants; young stars that are only millions of years old, which would have come from the recent starburst (more information on this later when we go into the spectrum of Minkowski’s Object). Also, Minkowski’s object happens to be the same size as the width of the radio jet!

Their paper estimates that the vast majority of the stars within Minkowski’s Object formed between 7 and 8.5 million years, with the burst of star formation beginning in the central region before spreading outwards.

A wider view of the area surrounding the Object -


A zoomed image on the area around Minkowski’s Object displaying the same data.


The object sits near the 'tip' of a large radio lobe emerging from the nucleus of NGC 0541. This can be clearly seen in the NRAO radio image of the Object and the surrounding area: -

Credit: NRAO\Aladin
The radio source emerging from the nucleus of NGC 0541 (PKS 0123-016A) is actually another small 'head and tail' source - i.e. it has two lobes - however only the western lobe extends beyond the edge of the galaxy's disk. The Eastern lobe can't be seen in the NRAO\Aladin Image but can be clearly seen as the pink loop on the right hand side of the images sourced from the paper by Croft et al. (2006)

The two large, and very bright radio features are not directly involved with Minkowski’s Object. They are produced by 3C 40 - the designation given to NGC 0547 by radio astronomers when dealing with it as a radio galaxy.2  (which is also known as PKS 0123-016B, Astrophysics where one name just isn't enough  :D) - as it interacts with NGC 0545.

As you can see the radio lobes belonging to NGC 0545 are massive! Some radio lobes can reach up to millions of light years like this galaxy’s pair, though the ones belonging to NGC 0541 are ‘only’ hundreds of thousands of light years in length.  The strength of the radio emissions of NGC 0545 makes it a type FR II galaxy, which is the more powerful of the two types of radio galaxy out there. The weaker radio emissions coming from the galaxy that lit up Minkowski’s Object belong to type FR I, the weaker of the two.

Minkowski’s Object is also very bright in U-V radiation, indicative of young high mass stars. Indeed as data from NASA's Galaxy Evolution Explorer - GALEX - shows it is the brightest source of UV radiation within Abell 0194. I have overlaid the DSS wide view image of the area with the appropriate GALEX data.

Credit: DSS\Aladin & NASA, GALEX (ND Filter)

The highest resolution image currently obtained of the object is, as one may expect, an image provided by the Hubble Space Telescope. The Minkowski Object was not the primary target of the image but it was in the right area of the sky to be captured as a lucky extra.
The image shows the two main areas of star formation - the large bright blobs - and the more diffuse regions trailing away from the main Object itself.

Credit: Hubble Legacy Archive and thanks to Professor Keel for providing us with this image

A spectrum for Minkowski’s Object

As you can see it shows the typical high emission peaks in doubly ionised oxygen and excited hydrogen that are typical of Starburst galaxies. The 2006 paper by Croft et al. puts the current rate of star formation in Minkowski’s Object at 0.5 solar masses per year with an uncertainty of 30% either way giving an overall star formation rate between 0.35-0.65 solar masses per year. To put that in perspective, the Milky Way churns out somewhere between 1 and 6 solar masses of star's per year. Given that Minkowski’s Object is around 1% the mass of the Milky Way it is forming a lot of stars for such a small clump of gas. The spectrum would suggest that the star formation rate could have been much higher at its peak.
Indeed it matches the spectrum of the prototype starburst galaxy  NGC 7714 which you can see below.



1 Rudolph Minkowski was a German-American astronomer who lived between 1895 and 1976. He is most well known for his work on supernovae, as he along with Walter Baade identified the distinction in the light curves of supernovae and divided them into Type I and Type II accordingly. He was also in charge of the National Geographic Society - Palomar Observatory Sky Survey. This conducted a photographic survey of the entirety of the Northern Sky as South as declination -220. He also discovered the planetary nebula M2-9 (More commonly known as the Butterfly Nebula ) and co-discovered the asteroid 1620 Geographos. He also worked at identifying the optical counterparts to radio sources and it was in this line of his work he discovered the Minkowski’s Object. In recognition of his work he was awarded the Bruce Medal for lifelong contributions to Astronomy in 1961 and has a crater on the moon named jointly after himself and his uncle Hermann Minkowski, who incidentally was the first to realise that Einstein's equations for Special Relativity could be best understood if one looked at them in 4 dimensions - considering time as a fourth spatial dimension and creating Minkowski Spacetime. A busy man (with a very busy Uncle) indeed  :o

2A radio galaxy is a class of AGN; a galaxy with a supermassive black hole with a penchant for accretion disks. The friction and magnetic fields within the disk collimates the radiation being emitted in massive quantities, sending it out in relativistic jets along the black holes axis.

The different types of AGN mostly depend on the angle in which you view the galaxy and its jets, and in this case the jets are at 90 degrees, straddling each side of the galaxy. The other thing that classifies a radio source is if its emission of radio waves reaches and exceeds 10^8 solar luminosities (a solar luminosity is the total light emitted from the sun per second)!

Sources and further reading: -

Minkowski's Object - A starburst triggered by a radio jet van Breugel et al. 1985
Minkowski's Object: A Starburst Triggered by a Radio Jet, Revisited. Croft et al. 2006

Peter stumbled on Minkowski’s Object whilst browsing on the SDSS database looking for interesting objects, it just goes to show you never know what you can find. :D

Hannah and I hope you have enjoyed this OOTD have as much as we did compiling and editing the images and information, until next time ;D
« Last Edit: May 01, 2011, 11:53:11 am by Lightbulb500 »

mitch

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Re: Saturday 30th April - Minkowski’s Object
« Reply #1 on: April 30, 2011, 04:50:36 pm »
Wow, LB & Hannah - what a terrific OOTD, best one you've done yet (IMHO) - congrats on all your hard work and making it readable to a duffer like me  8) 8) 8) ;D ;D ;D

Lightbulb500

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Re: Saturday 30th April - Minkowski’s Object
« Reply #2 on: April 30, 2011, 04:54:43 pm »
Thanks Mitch that means a lot ;D

lpspieler

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Re: Saturday 30th April - Minkowski’s Object
« Reply #3 on: April 30, 2011, 06:18:22 pm »
That's really in-depth! Wow.  :o Thanks for the great work.  ;D

echo-lily-mai

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Re: Saturday 30th April - Minkowski’s Object
« Reply #4 on: April 30, 2011, 06:44:37 pm »
You two, this is brilliant! 8) So much info and a really nice read  8)

Art does not reproduce the visible....  Paul Klee

Lightbulb500

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Re: Saturday 30th April - Minkowski’s Object
« Reply #5 on: April 30, 2011, 07:04:50 pm »
Thanks very much you two ;D ;D

Edit: - I just fixed a few grammar mistakes and typos that had evaded detection  >:(
« Last Edit: April 30, 2011, 07:37:29 pm by Lightbulb500 »

JohnF

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Re: Saturday 30th April - Minkowski’s Object
« Reply #6 on: April 30, 2011, 07:39:58 pm »
Looks a lot of research, well done you two.
John C. Fairweather - http://www.jcfwebsite.co.uk

Lightbulb500

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Re: Saturday 30th April - Minkowski’s Object
« Reply #7 on: April 30, 2011, 07:49:36 pm »
It was :D and thanks ;D

garrett_cw

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Re: Saturday 30th April - Minkowski’s Object
« Reply #8 on: May 01, 2011, 03:44:36 am »
Very good!  ;D
Curtis
"To get along in life you must be very clever or very nice. I've been clever. I recomend nice."

Lightbulb500

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Re: Saturday 30th April - Minkowski’s Object
« Reply #9 on: May 01, 2011, 10:15:21 am »
Thanks ;D

Geoff

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Re: Saturday 30th April - Minkowski’s Object
« Reply #10 on: May 01, 2011, 10:43:25 am »
One of the best OOTDs this year - very interesting and well researched.

I think there's a typo in this paragraph:

"Minkowski’s Object used to be part of the Intergalactic medium surrounding NGC 0514,"

should "0514" be "0541"?

"0514" occurs twice in the paragraph.
« Last Edit: May 01, 2011, 10:49:29 am by Geoff »
  Sometimes I think we're alone. Sometimes I think we're not. In either case, the prospect is staggering!- Arthur C. Clarke

stellar190

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Re: Saturday 30th April - Minkowski’s Object
« Reply #11 on: May 01, 2011, 10:50:17 am »
Oops, that'll teach me about writing at 4:30am ::) :D

Geoff

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Re: Saturday 30th April - Minkowski’s Object
« Reply #12 on: May 01, 2011, 10:58:43 am »
Just found another one!

"though the ones belonging to NGC 0514 are ‘only’ hundreds of thousands of light years in length. "

I think that's the last one  ;)
  Sometimes I think we're alone. Sometimes I think we're not. In either case, the prospect is staggering!- Arthur C. Clarke

Lightbulb500

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Re: Saturday 30th April - Minkowski’s Object
« Reply #13 on: May 01, 2011, 11:26:59 am »
Deary me :D

I'll get those fixed now, and thanks Geoff ;D

djj

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Re: Saturday 30th April - Minkowski’s Object
« Reply #14 on: May 01, 2011, 11:51:00 am »
Typos notwithstanding, an excellent OOTD, LB and Stellar 8) 8) 8), that I shall enjoy re-reading and inwardly digesting when I'm wider awake than I am at the moment :o. Have a nice relaxed bank holiday tomorrow following your labours :D :D :D.