APOD: Starburst Galaxy M94 from Hubble (2019 Dec 01)

[APOD Robot]

Starburst Galaxy M94 from Hubble

Explanation: Why does this galaxy have a ring of bright blue stars? Beautiful island universe Messier 94 lies a mere 15 million light-years distant in the northern constellation of the Hunting Dogs (Canes Venatici). A popular target for Earth-based astronomers, the face-on spiral galaxy is about 30,000 light-years across, with spiral arms sweeping through the outskirts of its broad disk. But this Hubble Space Telescope field of view spans about 7,000 light-years across M94's central region. The featured close-up highlights the galaxy's compact, bright nucleus, prominent inner dust lanes, and the remarkable bluish ring of young massive stars. The ring stars are all likely less than 10 million years old, indicating that M94 is a starburst galaxy that is experiencing an epoch of rapid star formation. The circular ripple of blue stars is likely a wave propagating outward, having been triggered by the gravity and rotation of a oval matter distributions. Because M94 is relatively nearby, astronomers can better explore details of its starburst ring.

<< Previous APOD

This Day in APOD

Next APOD >>

[Ann]

M94 has been one of my favorite galaxies since I saw a picture of it in James D Wray's A Color Atlas of Galaxies. The blue ring of M94 is very striking in Wray's atlas, and fascinatingly, the stellar population inside the blue ring is slightly greenish in Wray's book. But the innermost part of the inner region is yellow in Wray's picture. And lo and behold, the same color distribution is faintly visible here, too!

I'd say that the faintly greenish color of the outer part of the innermost region is due to the non-negligible presence of F-type and maybe even A-type stars. Or in other words, this part of the inner region contains many intermediate-aged stars, coupled, of course, with lots of old (and also young) red stars of spectral classes K and M.

I love this Hubble picture of M94 and the way it resolves the blue (and a few red) stars in the ring. I find it so delicate and beautiful.

I used to think that M94 was a very small galaxy indeed, only 35,000 light-years in diameter, which would make it tiny indeed and smaller than M33, for example. But according to this site, the diameter of M94 is 50,000 light-years, which still makes it a lot smaller than the Milky Way, but not exceedingly tiny.

Ann

[orin stepanek]

A star speckled beauty!

M94_Hubble_960.jpg (54.36 KiB) Viewed 7911 times

[sillyworm 2]

Would someone please describe Oval Mass Distribution for me? I could not find a decent explanation.

[sillyworm 2]

I meant Oval Matter Distributions.I cannot find an edit button.

[neufer]

Milky Way Galaxy Spiral Arms – based on WISE data.

---

Would someone please describe Oval Matter Distribution for me?

Oval Matter Distributions like the bar at the center of the Milky Way
that displays a constant rotation rate (emulating a rigid body)

...unlike the surrounding arms of the Milky Way
in which stars like the Sun orbit at a constant velocity.

[heehaw]

It is extremely irritating that, apparently, Andromeda does not have a bunch of hundred-million-year-old civilizations who are doing their moral duty, by continuously bombarding our galaxy with historical atlases of the appearance of our galaxy, from their galaxy, over the past hundreds of millions of years. Sigh!

[neufer]

It is extremely irritating that, apparently, Andromeda does not have a bunch of hundred-million-year-old civilizations who are doing their moral duty, by continuously bombarding our galaxy with historical atlases of the appearance of our galaxy, from their galaxy, over the past hundreds of millions of years. Sigh!

---

<<UGC 12158 or PGC 69533 is an Sb-type barred spiral galaxy located approximately 384 Mly away from Earth in the constellation of Pegasus. Its tight spiral disk spans approximately 140,000 ly across. It is also often stated to resemble the Milky Way in appearance, which is mostly due to its disk inclination being almost perpendicular to the line of sight.

https://www.discovermagazine.com/the-sc ... more-25551

On 15 December 2003, a 19.2v magnitude Type Ia supernova, was recorded on one of the spiral arms near the apparent centre in UGC 12158, and was designated as SN 2004EF. (Blue star within UGC 12158 in Starbox Hubble's Space Telescope image.) It reached 17.5v magnitude on 4 September 2004 before fading from view. Optical spectra was obtained on 7 September 2014 confirming the Type I classification. No progenitor star was found on earlier survey images.>>

[Bill Bruehl]

I've never heard it discussed, but when I stare an image like this I see the galaxy observed as cone-shaped with the spiral leading down into the glowing center. I suspect that most naive observers - like me - imagine that galaxies are essentially flat when they are actually so deep that it would take light years to go from the top to the center bottom.

[neufer]

I've never heard it discussed, but when I stare [sic] an image like this I see the galaxy observed as cone-shaped with the spiral leading down into the glowing center. I suspect that most naive observers - like me - imagine that galaxies are essentially flat when they are actually so deep that it would take light years to go from the top to the center bottom.

You should really stop staring at images like this.

(When I snap my fingers you will awaken with no memory of this Asterisk* thread.)

[Chris Peterson]

I've never heard it discussed, but when I stare an image like this I see the galaxy observed as cone-shaped with the spiral leading down into the glowing center. I suspect that most naive observers - like me - imagine that galaxies are essentially flat when they are actually so deep that it would take light years to go from the top to the center bottom.

A better model (and one you can probably train yourself to see) is a spherical center surrounded by a thin disc. The spiral arms have a thickness on the order of 1% of the galaxy diameter. Pretty thin.

[neufer]

360-degree panorama view of the warped Milky Way disk

---

Click to play embedded YouTube video.

I suspect that most naive observers - like me - imagine that galaxies are essentially flat when they are actually so deep that it would take light years to go from the top to the center bottom.

A better model (and one you can probably train yourself to see) is a spherical center surrounded by a thin disc. The spiral arms have a thickness on the order of 1% of the galaxy diameter. Pretty thin.

The Milky Way consists of a bar-shaped core region
surrounded by a warped disk of gas, dust and stars.

Spiral galaxy ESO 510-G13 by Hubble Space Telescope

---

[RJN]

In response to emailed criticisms and discussion with noted astronomer John Kormendy, I have adapted the text on the main NASA APOD page. Specifically, I deleted the link to "density wave" under "wave propagating" since the (likely) outgoing wave is not a density wave. I have also added the phrase "from inspiraling gas" to indicate that the high density of matter near the center of M94 is due to mass that has been transported inward from the main disk. I apologize for the oversights. - RJN

[neufer]

In response to emailed criticisms and discussion with noted astronomer John Kormendy, I have adapted the text on the main NASA APOD page. Specifically, I deleted the link to "density wave" under "wave propagating" since the (likely) outgoing wave is not a density wave. I have also added the phrase "from inspiring gas" to indicate that the high density of matter near the center of M94 is due to mass that has been transported inward from the main disk:

• The ring stars are all likely less than 10 million years old, indicating that M94 is a starburst galaxy that is experiencing an epoch of rapid star formation from inspiring gas.

inspiraling (v.) (present participle of inspiral: From in- +‎ spiral. ) (astronomy) To spiral inward.

spiral: 1550s, from Middle French spiral (16c.), from Medieval Latin spiralis "winding around a fixed center, coiling" (mid-13c.), from Latin spira "a coil, fold, twist, spiral," from Greek speira "a winding, a coil, twist, wreath, anything wound or coiled." Related: Spirally. Spiral galaxy first attested 1913.

<<inspire (v.) mid-14c., enspiren, "to fill (the mind, heart, etc., with grace, etc.);" also "to prompt or induce (someone to do something)," from Old French enspirer (13c.), from Latin inspirare "blow into, breathe upon," figuratively "inspire, excite, inflame," from in- "in" + spirare "to breathe."

The Latin word was used as a loan-translation of Greek pnein in the Bible. General sense of "influence or animate with an idea or purpose" is from late 14c. Also sometimes used in literal sense in Middle English. Related: Inspires; inspiring.>>

[orin stepanek]

I meant Oval Matter Distributions.I cannot find an edit button.

The edit button is the pen shaped image next to the quote image and report button! (an exclamation mark in a square) and also a delete button! An X in a square!

[neufer]

I meant Oval Matter Distributions.I cannot find an edit button.

The edit button is the pen shaped image next to the quote image and report button!
(an exclamation mark in a square) and also a delete button! An X in a square!

So what's the pencil shaped image, then?

(Why not a Sharpie shaped image to edit the posts of others?)

[ems57fcva]

That so-called ring is an illusion. What I am seeing is the central bulge of the galaxy, with its inner part being obscured by infalling gas and dust.

[Ann]

Would someone please describe Oval Mass Distribution for me? I could not find a decent explanation.

Naaah. The APOD caption writer was being funny.

I googled "oval matter" and found a lot of ear pads and locket pendants. Oh, and I found the Hubble picture of M94, too.

Ann

[Bugui]

Hello!. Thanks for the beautiful image and for the explanations. I have one basic question: If the blue dots on the other ring are stars, why don't we see yellow dots on the center region? or in the middle region? I understand that all that yellow light is created by thousands of stars...
Thanks again!

[Ann]

Hello!. Thanks for the beautiful image and for the explanations. I have one basic question: If the blue dots on the other ring are stars, why don't we see yellow dots on the center region? or in the middle region? I understand that all that yellow light is created by thousands of stars...
Thanks again!

Click to view full size image

NGC 602, star formation in the Small Magellanic Cloud.
Photo: X-ray: NASA/CXC/Univ.Potsdam/L.Oskinova et al; Optical: NASA/STScI;
Infrared: NASA/JPL-Caltech.

The short answer is that the blue stars in the ring are young, but the yellow stars in the center are old.

Take a look at the picture at left, which shows star formation in the Small Magellanic Cloud. You can see a group of perhaps seven bright blue stars at upper right. These stars are hot, bright and blue, just like the blue stars in the ring of M94. The stars are also very massive, probably at least eight times as massive as the Sun, and possibly as much as 50-100 times as massive as the Sun. Such massive stars die very young, because they burn their "fuel" at a furious rate.

Click to view full size image

Young star cluster NGC 3293. Photo: ESO/G. Beccari.

The stars of NGC 602 in the Small Magellanic Cloud are very young, younger than the blue stars of the ring of M94. We can compare the bright stars of M94 with the bright stars of cluster NGC 3293. Look at the picture at right. As you can see, one of the stars in the cluster is orange. This star has turned into a red giant. The orange star has used up the hydrogen in its core, which is any star's prime fuel. When a star has used up its core hydrogen, it begins to die. Usually, the first step of dying is swelling up into a red giant. You can see, if you look at the Hubble picture of M94, that red stars are mixed with the blue stars in the ring. The red stars are red giants.

The more massive a star is, the faster it uses up all its fuel and the faster it dies. Very massive stars die in supernova explosions, which completely destroy the star.

Click to view full size image

NGC 602 in the Small Magellanic Cloud. ESA/Hubble.

Click to view full size image

Stars of globular cluster NGC 6752 with background galaxy.
ESA - Hubble, NASA, Bedin et al

Take a look at the picture of NGC 602 again. Can you see that there are very many fainter stars close to the bright ones? These fainter stars were formed in the same burst of star formation that formed the brighter stars. But the fainter stars will live on long, long after the bright ones are gone.That is because the fainter stars are much less massive than the bright ones, and the less massive a star is, the longer it will live. And: The less massive a star is, the redder it is.

Take a look at the picture of globular cluster NGC 6752. There is a background galaxy peeking through the globular at left, but you can ignore it. But please note that the fainter the stars in the cluster are, the redder they are.

So why is the inner part of M94 yellow, and why can't we see individual yellow stars in it? It is because the stars in the center of M94 are so numerous, so relatively faint and so yellowish. Take a look at stars in the globular cluster again. Not all of the stars are red, and the overall, "composite" color of all the stars in the center of M94 is yellow.

Click to view full size image

Sapphires. Fotos Libres de Derechos.

Click to view full size image

Grains of sand.

You can think of the blue stars in the ring of M94 as brilliant sapphires. But the yellow stars in the center of M94 are like age-old grains of sand.

Ann

[neufer]

You can think of the blue stars in the ring of M94 as brilliant sapphires.
But the yellow stars in the center of M94 are like age-old grains of sand.

---

To see a world in a grain of sand
And a heaven in a wild flower,
Hold infinity in the palm of your hand,
And eternity in an hour.

"Auguries of Innocence" is a poem from one of William Blake's notebooks now known as The Pickering Manuscript. It is assumed to have been written in 1803, but was not published until 1863 in the companion volume to Alexander Gilchrist's biography of William Blake. The poem contains a series of paradoxes which speak of innocence juxtaposed with evil and corruption. The poem is 132 lines and has been published with and without breaks that divide the poem into stanzas. An augury is a sign or omen.

[orin stepanek]

And someone said there are more stars in the universe than grains of sand on the beach!

[neufer]

And someone said there are more stars in the universe than grains of sand on the beach!

Click to play embedded YouTube video.

<<The Sand Reckoner (Greek: Ψαμμίτης, Psammites) is a work by Archimedes in which he set out to determine an upper bound for the number of grains of sand that fit into the Universe. In order to do this, he had to estimate the size of the universe according to the contemporary model, and invent a way to talk about extremely large numbers. The work, also known in Latin as Archimedis Syracusani Arenarius & Dimensio Circuli, which is about eight pages long in translation, is addressed to the Syracusan king Gelo II (son of Hiero II), and is probably the most accessible work of Archimedes; in some sense, it is the first research-expository paper.

• There are some, king Gelon, who think that the number of the sand is infinite in multitude; and I mean by the sand not only that which exists about Syracuse and the rest of Sicily but also that which is found in every region whether inhabited or uninhabited. Again there are some who, without regarding it as infinite, yet think that no number has been named which is great enough to exceed its magnitude. And it is clear that they who hold this view, if they imagined a mass made up of sand in other respects as large as the mass of the Earth, including in it all the seas and the hollows of the Earth filled up to a height equal to that of the highest of the mountains, would be many times further still from recognizing that any number could be expressed which exceeded the multitude of the sand so taken. But I will try to show you by means of geometrical proofs, which you will be able to follow, that, of the numbers named by me and given in the work which I sent to Zeuxippus, some exceed not only the number of the mass of sand equal in magnitude to the Earth filled up in the way described, but also that of the mass equal in magnitude to the universe.
  — Archimedis Syracusani Arenarius & Dimensio Circuli

Which Is Greater, The Number Of Sand Grains On Earth Or Stars In The Sky?
Robert Krulwich, NPR, September 17, 201210

<<Here's an old, old, question, but this time with a surprise twist. The question is — and I bet you asked it when you were 8 years old and sitting on a beach: Which are there more of — grains of sand on the Earth or stars in the sky? Science writer David Blatner, in his new book Spectrums, says a group of researchers at the University of Hawaii, being well-versed in all things beachy, tried to calculate the number of grains of sand. They said, if you assume a grain of sand has an average size and you calculate how many grains are in a teaspoon and then multiply by all the beaches and deserts in the world, the Earth has roughly 7.5 x 10¹⁸ grains of sand.>>

How many stars are there in the Universe?
ESA / Science & Exploration / Space Science / Herschel

<<It has been said that counting the stars in the Universe is like trying to count the number of sand grains on a beach on Earth. We might do that by measuring the surface area of the beach, and determining the average depth of the sand layer. For the Universe, the galaxies are our small representative volumes, and there are something like 1011 to 1012 stars in our Galaxy, and there are perhaps something like 10¹¹ or 10¹² galaxies. With this simple calculation you get something like 10²² to 10²⁴ stars in the Universe.

ESA's infrared space observatory Herschel has made an important contribution by 'counting' galaxies in the infrared, and measuring their luminosity in this range – something never before attempted. Knowing how fast stars form can bring more certainty to calculations. Herschel has also charted the formation rate of stars throughout cosmic history. If you can estimate the rate at which stars have formed, you will be able to estimate how many stars there are in the Universe today. In 1995, an image from the Hubble Space Telescope (HST) suggested that star formation had reached a peak at roughly seven thousand million years ago. Recently, however, astronomers have thought again. The Hubble Deep Field image was taken at optical wavelengths and there is now some evidence that a lot of early star formation was hidden by thick dust clouds. Dust clouds block the stars from view and convert their light into infrared radiation, making them invisible to the HST. But Herschel could peer into this previously hidden Universe at infrared wavelengths, revealing many more stars then ever seen before.

Gaia will study one thousand million stars in our Milky Way. It will build on the legacy of the Hipparchus mission, which pinpointed the positions of more than one hundred thousand stars to high precision, and more than one million stars to lesser precision. Gaia will monitor each of its one billion target stars 70 times during a five-year period, precisely charting their positions, distances, movements, and changes in brightness. Combined, these measurements will build an unprecedented picture of the structure and evolution of our Galaxy.>>

[neufer]

---

Unveiling the Nature of M94’s (NGC4736) Outer Region:
a Panchromatic Perspective

Ignacio Trujillo, Inma Martinez-Valpuesta and David Martínez-Delgado ( IAC), Jorge Peñarrubia (Institute of Astronomy, Univ. of Cambridge), R. Jay GaBany (Blackbird Observatory), Michael Pohlen (Cardiff)

<<We have conducted a deep, multiwavelength analysis to study the outer region of the nearby galaxy, M94 (NGC4736). We found that non-optical data supports the idea that the outskirts of this galaxy were not formed by a closed stellar ring, as traditionally claimed in the literature, but by an extensive structure of spiral arms.

In this sense, M94 (NGC4736) is a good example of a Type III galaxy with a bright outer disk. Significantly, we found that the outer disk of this galaxy is active. It contains approximately 23% of the galaxy's total stellar mass and contributes about 10% of the galaxy's new stars. In fact, the star formation rate of the outer disk is approximately two times greater than the inner disk because it is more efficient per unit of stellar mass.

There are several possible external events that could have led to the origin of M94's outer disk including the accretion of a satellite galaxy or the gravitational interaction with a nearby star system. However, our research found problems with each of these scenarios. So, we looked for an internal explanation and that approach produced the most plausible result. Therefore, we strongly suspect that the inner disk of M94 (NGC4736) is an oval distortion which led to the creation of this galaxy's peripheral disk.>>

[Bugui]

Hello!. Thanks for the beautiful image and for the explanations. I have one basic question: If the blue dots on the other ring are stars, why don't we see yellow dots on the center region? or in the middle region? I understand that all that yellow light is created by thousands of stars...
Thanks again!

Click to view full size image

NGC 602, star formation in the Small Magellanic Cloud.
Photo: X-ray: NASA/CXC/Univ.Potsdam/L.Oskinova et al; Optical: NASA/STScI;
Infrared: NASA/JPL-Caltech.

The short answer is that the blue stars in the ring are young, but the yellow stars in the center are old.

Take a look at the picture at left, which shows star formation in the Small Magellanic Cloud. You can see a group of perhaps seven bright blue stars at upper right. These stars are hot, bright and blue, just like the blue stars in the ring of M94. The stars are also very massive, probably at least eight times as massive as the Sun, and possibly as much as 50-100 times as massive as the Sun. Such massive stars die very young, because they burn their "fuel" at a furious rate.

Click to view full size image

Young star cluster NGC 3293. Photo: ESO/G. Beccari.

The stars of NGC 602 in the Small Magellanic Cloud are very young, younger than the blue stars of the ring of M94. We can compare the bright stars of M94 with the bright stars of cluster NGC 3293. Look at the picture at right. As you can see, one of the stars in the cluster is orange. This star has turned into a red giant. The orange star has used up the hydrogen in its core, which is any star's prime fuel. When a star has used up its core hydrogen, it begins to die. Usually, the first step of dying is swelling up into a red giant. You can see, if you look at the Hubble picture of M94, that red stars are mixed with the blue stars in the ring. The red stars are red giants.

The more massive a star is, the faster it uses up all its fuel and the faster it dies. Very massive stars die in supernova explosions, which completely destroy the star.

Click to view full size image

NGC 602 in the Small Magellanic Cloud. ESA/Hubble.

Click to view full size image

Stars of globular cluster NGC 6752 with background galaxy.
ESA - Hubble, NASA, Bedin et al

Take a look at the picture of NGC 602 again. Can you see that there are very many fainter stars close to the bright ones? These fainter stars were formed in the same burst of star formation that formed the brighter stars. But the fainter stars will live on long, long after the bright ones are gone.That is because the fainter stars are much less massive than the bright ones, and the less massive a star is, the longer it will live. And: The less massive a star is, the redder it is.

Take a look at the picture of globular cluster NGC 6752. There is a background galaxy peeking through the globular at left, but you can ignore it. But please note that the fainter the stars in the cluster are, the redder they are.

So why is the inner part of M94 yellow, and why can't we see individual yellow stars in it? It is because the stars in the center of M94 are so numerous, so relatively faint and so yellowish. Take a look at stars in the globular cluster again. Not all of the stars are red, and the overall, "composite" color of all the stars in the center of M94 is yellow.

Click to view full size image

Sapphires. Fotos Libres de Derechos.

Click to view full size image

Grains of sand.

You can think of the blue stars in the ring of M94 as brilliant sapphires. But the yellow stars in the center of M94 are like age-old grains of sand.

Ann

Thanks!!!