Dwarf galaxies discovered

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brian livesey
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Dwarf galaxies discovered

Post by brian livesey »

Our Milky Way galaxy has a number of dwarf galaxies orbiting it, and another nine have recently been discovered.
These dwarf galaxies, ranging from 95,000 light years to a million light years distant, went unnoticed because of their extreme faintness. But two teams of astronomers from Cambridge and Fermi Lab in the USA, working independently, detected the galaxies while using extremely sensitive instruments in the southern sky designed to search for dark matter. The dwarves were found near the Large and Small Magellanic Clouds and with a powerful digital camera able to detect the glow of galaxies eight billion light years from Earth:
"Dwarf satellites are the final frontier for testing our theories of dark matter. We need to find them to determine whether our cosmological picture makes sense," said Vasily Belokurov of the Institute of Astronomy at Cambridge.
"Finding such a large group of satellites near the Magellanic Clouds was surprising, as earlier surveys of the southern sky found very little, we were not expecting to stumble on such a treasure," added Dr. Belokurov.
Three of the nine objects are definitely dwarf galaxies said the Cambridge team, but the others could either be dwarf galaxies or globular clusters. Dwarf galaxies contain only a few thousand stars, compared to the many billions in our galaxy.
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Cliff
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Re: Dwarf galaxies discovered

Post by Cliff »

Dear Brian
From what I recall, it was once thought M31 was similar in size to our Milky Way galaxy. A bit more recently it was suggested M31 was a bit bigger than the Milky Way. Then
I think I read somewhere (?) a few weeks ago that because there are (or were) more dwarf galaxies associated with M31 than dwarf galaxies associated with our "milky way" galaxy, M31 might be very much bigger than our galaxy.
But if more dwarf galaxies have now been found associated with the Milky Way, possibly M31 isn't the biggest - or at least not that much bigger after all ???
Best wishes from Cliff
brian livesey
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Re: Dwarf galaxies discovered

Post by brian livesey »

It's interesting what you say about M31 Cliff. Another technique has recently been used on this Andromeda spiral to reveal more mass in the galaxy.
The current NEW SCIENTIST (p.19) refers to a technique known as "quasar backlighting". Researchers in America have studied how the light from 18 background quasars interacts with sodium in the outer halo of M31:
"We found at least 40 billion solar masses in the gaseous halo," says Nicolas Lehner of the University of Notre Dame, Indiana - a marked increase in the amount of ordinary matter in the galaxy.
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Cliff
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Re: Dwarf galaxies discovered

Post by Cliff »

Dear Brian
You made some more interesting comments (1st April) about M31. However, you referred to the current New Scientist p19. I already had 28th March NS but can't see anything on p19 about M31 in that. Today (2nd April) I got the latest 4th April New Scientist - andbut not in that.
Possibly the current NS you referred to, might be 21st March NS ?Whatever, I assume Nicholas Lehner (Notre Dame Uni) suggests the 40 billion solar masses is the total amount of ordinary gaseous matter in the M31 halo - not that the 40 billion solar masses is additional to an amount of ordinary gaseous matter known in the halo before ? Just to add to my confusion I suppose there may also be a wee bit of dark matter some where involved as well ??
Best of luck from Cliff
brian livesey
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Re: Dwarf galaxies discovered

Post by brian livesey »

You're right Cliff, the article was in the March 21st edition of NS. I was away on the Emerald Isle last week and got the dates mixed up.
The extra mass discovered is described in the article as "regular matter", not dark matter.
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Cliff
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Re: Dwarf galaxies discovered

Post by Cliff »

Dear Brian
Thanks for clarifying the NS magazine date problem. Incidentally I'm sorry I probably only confused things mentioning dark matter, but I think I've read somewhere that M31 probably contains some dark matter, but not how much of it there actually is.
I hope you enjoyed your trip to the Emerald Isle, the farthest I ever got across the Irish Sea was the Isle of Man. However, I reckon I once saw Ireland from near the top of Carnedd Lliwelyn (hope I spelt that right) in amazing conditions.
from Cliff
brian livesey
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Re: Dwarf galaxies discovered

Post by brian livesey »

I have a HELIOS 40mm, 10-25X, monocular Cliff that's handy for basic astronomy, although the eye lens could have been bigger in diameter.
The monocular comes in handy for ship-spotting, too. Halfway across the Irish sea on the Holyhead-Dublin ferry, I was able to see the Welsh mountains on one side and the Dublin hills on the other, and on the lowest magnification.
Last edited by brian livesey on Thu Apr 09, 2015 2:52 pm, edited 1 time in total.
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Cliff
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Re: Dwarf galaxies discovered

Post by Cliff »

Dear Brian
Using an atlas I got the distance Holyhead to Dublin - 68 miles. Many years ago I saw the Isle of Man about 60 miles away (highest point Snaefell 625 metres) by unaided eye, several times from Blackpool. I notice that Djouce Mountain - about 886 metres high, south of Dublin is like that city, also about 68 miles from Holyhead and so might be visible from the towns vicinity. However, I think Holyhead faces NNE so it might be necessary to go to high ground behind the town to see Djouce Mt.(?).
You mentioned your monocular. I got a small telescope about 1 inch aperture for my birthday when I was a youngster. It provided X20 magnification, views of Galilean Satellites but I never saw Saturn's rings. Thinking about it got me wondering when binoculars were first used for amateur astronomy. "Practical Amateur Astronomy" (1963) doesn't seem to mention using binoculars at all. I think it may have been American astronomers who first used ordinary binoculars (?).
Best wishes from Cliff
brian livesey
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Re: Dwarf galaxies discovered

Post by brian livesey »

Correct me if I'm mistaken Cliff, but the prismatic binocular ( in contrast to the Galilean field-glass ) was a German innovation, so, "serious" binocular astronomy might have started there.
Incidently, last week on a local flea-market, I bought a pair of GREEN CAT 8X40 bins of the American moulded-body type. The optics are in pristine condition, giving sharp definition almost to the edge of the field, and no discernible marks on the leatherette body.
The problem with the bins was that the rotating cup for the adjustable eyepiece was missing, but I happened to have a spare cup that fits perfectly.
The bins are light and very comfortable to use for astronomy. Price? £3 :D .
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mike a feist
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Re: Dwarf galaxies discovered

Post by mike a feist »

Although not mentioned in astronomy books,Cliff, in the past, does not, of course, mean that binoculars were not used for amateur astronomy/skywatching. As a parallel line of thought...how many astronomy guides start of with the mention (often disparagingly) with the Galilean opera-glass,then consider the binocular and its uses, and then launching into the refractor, then the reflector and catadioptics, etc without mentioning the prismatic telescope - the terrestrial spotting scope?! regards mike
Cliff
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Re: Dwarf galaxies discovered

Post by Cliff »

Dear Brian & Mike
Thanks - I read just recently (Wikipedia I think) that when Hans Lippershey applied to patent "his" telescope (1608) a bureaucrat asked Lippershey stick two scopes together side by side (effectively a binocular). It isn't made clear whether or not Lippershey actually did it (?) and needless to say I feel pretty sure he didn't invent the telescope .
I gather opera glasses (cheap bins!) became popular after 1825 for theatre \ opera goers (possibly a German idea as Brian suggested).
I don't have many old astronomy books . However, my copy of "The Story of the Heavens" originally written by (Sir) Robert Ball (1886), page 27 says -
"The most suitable instrument for commencing astronomical studies is within ordinary reach. It is the well known binocular that a captain uses on board ship; or If that cannot be had, then the common opera glass will answer nearly as well."
Unfortunately my copy of Ball's book doesn't seem to be a first edition. because it contains mention of observations made in 1898. So the mention of bins & opera glasses may have been added after 1886. Even so it seems to suggest binoculars were recommended for astronomy perhaps before 1900 at least.
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Re: Dwarf galaxies discovered

Post by brian livesey »

Pity the bins were locked away on the Titanic. :wink:
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Cliff
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Re: Dwarf galaxies discovered

Post by Cliff »

Dear Brian
Funny you mention the Titanic - only last week I got "I survived the Titanic" by Lawrence Beesley (a surviving passenger !!!). I've only skimpted into the book as yet. However, I'm not sure how reliable Beesley was. Apparently some suvivors (one being Jack Sayer soon after being rescued) said the Titanic broke in two when it went down but Beesley seems to have been adamant it didn't - but recent "modern" investigations have found the Titanic in two bits at the bottom of the Atlantic (strongly suggesting Sayer & others had been right).
By the way I've been thinking of selling some old binoculars which my Grandad might have used to watch the Titanic sink (whilst watching Kate Winslet & L DiCaprio on TV in "Titanic".
Incidentally I now think my "Story of the Heavens" is a genuine first edition - Wikipedia seems to suggest the book wasn't published until 1900 although the Preface in mine was written by Ball in 1886.
Best wishes from Cliff (PS I wonder if Beesley had any ideas about Cosmology ?)
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