Universe Today

May 11, 2009December 24, 2015 by Fraser Cain

Galactic Plane

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The Milky Way is a vast spiral galaxy, shaped a bit like a spinning record; just one that measures 100,000 light-years across and only 1,000 light-years thick. Imagine you were below the Milky Way, and passed through the disk of stars above it. That moment when you’re halfway through the 1,000 light-year thickness of stars? That’s the galactic plane.

Astronomers actually use a coordinate system to measure positions in the Milky Way, starting with the Sun as the center point. No, we’re not actually at the center of the Milky Way, we’re actually off to the side, but this makes the measurement easier. They draw a line from the Sun to the center of the Milky Way, and that defines the 0-degree point, and then coordinates are measured within the galactic plane. You can have galactic latitude and longitude.

Have you heard anyone mention that the Sun is supposed to be crossing the galactic plane in 2012? Yeah, that’s a myth. Here’s the thing. The Sun does bob up and down in the galactic plane. Sometimes we’re above the plane, and then other times we’re below the plane. But that cycle takes 64 million years to complete! It’s impossible to define the exact moment of when the Solar System will pass exactly through the galactic plane.

And astronomers don’t think that anything special will happen when the Solar System does pass through the galactic plane. In fact, it’s the times when the Earth is above or below the galactic plane when we might be at risk. A recent scientific study correlated those times with large extinction events in the Earth’s history. It’s possible that the Milky Way’s magnetic field protects the Earth from intergalactic radiation and cosmic rays, and when we’re significantly above or below the galactic plane, life on Earth suffers more damage from space radiation.

But that’s just a theory.

So, to summarize, the Solar System won’t be passing through the galactic plane in 2012. There’s no easy way to know exactly when that’ll happen, and there’s absolutely no way to give that a specific date. And even when we do pass through the galactic plane, there’s no risk to our planet.

Here’s a link to an article on Universe Today about possible extinction events when the Earth is above or below the galactic plane.

If you’d like more info on galaxies, check out Hubblesite’s News Releases on Galaxies, and here’s NASA’s Science Page on Galaxies.

We have also recorded an episode of Astronomy Cast about galaxies – Episode 97: Galaxies.

Sources: EarthSky.org, NASA

May 11, 2009December 24, 2015 by Fraser Cain

Distance to Andromeda

Traveling to distant locations, like Andromeda, could have interesting consequences. Credit: NASA

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The distance to the Andromeda Galaxy is 2.54 million light-years, or 778 kiloparsecs.

The Andromeda Galaxy can be seen with the unaided eye, so skywatchers have been observing it for thousands of years. Charles Messier cataloged it as M31 in his 1764 list. Back then, astronomers thought that Andromeda was a nebula, and based on its size, Messier guessed that it was only about 2,000 times further than the star Sirius.

Astronomers discovered variable star called novae in Andromeda in 1917, and quickly realized that they were 10 times less bright than similar objects in the Milky Way. Astronomers Heber Curtis proposed that Andromeda was a separate “island universe”, located about 500,000 light-years away. Edwin Hubble ended the controversy once and for all in 1925 when he identified Cepheid variable stars in Andromeda, and calculated that the galaxy was actually 1.5 million light-years away.

Modern astronomers are continuing to calculate the distance to Andromeda. In 2003, astronomers calculated that Andromeda is 2.57 million light-years away. And in 2004, astronomers redid Hubble’s Cepheid variable calculations, and determined that Andromeda was 2.51 million light-years. Another group used a different technique in 2005 to calculate that Andromeda was 2.52 million light-years away. And yet another technique in 2005 put it at 2.56 million light-years away. And so, the agreed distance of 2.54 million light-years is an average of the distances measured so far.

There are several galaxies closer to Earth than Andromeda. The Large Magellanic Cloud is only 160,000 light years away, and the Canis Major Dwarf Galaxy is a mere 25,000 light-years from Earth. But Andromeda is the largest grand spiral galaxy to us.

We have written many articles about galaxies for Universe Today. Here’s another article about the closest galaxies to the Milky Way.

If you’d like more info on galaxies, check out Hubblesite’s News Releases on Galaxies, and here’s NASA’s Science Page on Galaxies.

We have also recorded an episode of Astronomy Cast about galaxies – Episode 97: Galaxies.

May 11, 2009December 24, 2015 by Fraser Cain

Galaxy Rotation

Artist's Conception of our Milky Way Galaxy: Blue, green dots indicate distance measurements. CREDIT: Robert Hurt, IPAC; Mark Reid, CfA, NRAO/AUI/NSF

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Look across the Universe, and you’ll see that almost everything is rotating. The Earth rotates on its axis as it orbits the Sun. And the Sun itself is rotating. As you can probably guess, we even have galaxy rotation with our Milky Way galaxy.

Our galaxy is rotating incredibly slowly, however. It takes the Sun 220 million years to complete a single orbit around the galaxy. In the 4.6 billion years that the Sun and planets have been here, they’ve only rotated around the center of the galaxy about 20 times.

We know that galaxy rotation is happening because the Milky Way is a flattened disk, in the same way that the Solar System is a flattened disk. The centrifugal force from the rotation flattens out the galactic disk. All stars in the galactic disk follow roughly circular orbits around the center of the galaxy. Stars in the halo can have much different orbits and speeds.

The calculation of the high rotational speed of the galaxy led to the discovery of dark matter. If our galaxy contained just the matter we can see – planets, gas, etc – the galaxy rotation should cause it to spin apart. Instead, there’s much more mass holding the galaxy together. In fact, astronomers have calculated that the total mass of the galaxy is probably 10 times greater than the sum of all the stars in it. 90% of this is invisible dark matter, holding the galaxy rotation together. And only 10% is the regular matter that we can see. Our galaxy really has a mass of more than 1 trillion suns, and extends out more than 600,000 light-years; a third of the distance to the nearby Andromeda galaxy.

All the galaxies we can see are rotating. It’s this rotational force that counteracts the inward pull of gravity from all the galaxies. If galaxies didn’t rotate, they’d collapse inward and just join the supermassive black holes at the hearts of galaxies.

We have written many articles about galaxies for Universe Today. Here’s another article about the rotation of the Milky Way.

If you’d like more info on galaxies, check out Hubblesite’s News Releases on Galaxies, and here’s NASA’s Science Page on Galaxies.

We have also recorded an episode of Astronomy Cast about galaxies – Episode 97: Galaxies.

References:
SEDS
http://www.astronomy.ohio-state.edu/~ryden/ast162_7/notes30.html

May 11, 2009December 24, 2015 by Fraser Cain

What is the Largest Galaxy?

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Galaxies can range in size from having just a few million stars to well over a trillion stars. But have you ever wondered, what’s the largest galaxy in the Universe. The Universe is a big place, and we’ll probably never be able to see every single galaxy. So we can never know for sure what the biggest galaxy is. Instead, we’ll have to go with, what’s the largest galaxy that we know of?

The largest galaxies in the Universe are the giant elliptical galaxies. These are large, egg-shaped galaxies with trillions of stars. They’re formed through multiple collisions between smaller spiral galaxies of similar size. For example, when our own Milky Way collides with the same sized Andromeda Galaxy in a few billion years, the outcome will probably be a giant elliptical galaxy, with about a trillion stars.

The galaxies that can get the largest are the ones at the very center of galaxy clusters. Astronomers call these cD galaxies (for giant diffuse galaxies), or bright cluster galaxies. The grow by gobbling up any galaxy that comes too close to them, and since they’re at the center of a galaxy cluster, many galaxies get too close. In fact, these galaxies have a large space around them where astronomers can’t find any smaller galaxies; they’ve all been consumed by the larger galaxy.

A large cD galaxy can be 10 times brighter than the Milky Way, with about 100 times as much mass. They can have a diameter of 6 million light-years across (the Milky Way is about 100,000 light-years across).

An example of this is the central galaxy in the cluster Abell 2029.

It’s probably that there are even larger galaxies out there. And if they are there, you’ll find them at the center of the largest galaxy clusters.

We have written many articles about galaxies for Universe Today. Here’s an article about research into the galaxy cluster Abell 2029.

If you’d like more info on galaxies, check out Hubblesite’s News Releases on Galaxies, and here’s NASA’s Science Page on Galaxies.

We have also recorded an episode of Astronomy Cast about galaxies – Episode 97: Galaxies.

May 11, 2009December 24, 2015 by Fraser Cain

Ring Galaxy

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There are spiral galaxies and elliptical galaxies, but one of the strangest you’re ever going to see is a ring galaxy. One of the most famous examples of these is Hoag’s Object, discovered in 1950 by Art Hoag – but there are other examples as well.

And a ring galaxy really does look like a ring. There’s a bright central core, and then a large gap without much luminous matter, and then a bright ring containing hot, blue stars.

Astronomers think that ring galaxies are formed when a smaller galaxy passes through the center of a larger galaxy. The space between stars in a galaxy is vast, so when galaxies collide, the stars don’t actually crash into each other. Instead, it’s their gravity that makes a mess. In this situation, it’s thought that the smaller galaxy slices right through the disk of the larger galaxy. The gravity of the smaller galaxy collapses vast clouds of gas and dust, and creates a burst of star formation around the edge of the larger galaxy.

The change in gravity drastically affects the orbit of the stars in the larger galaxy. They orbit outward and bunch up into the bright starforming ring. This blue ring is continuing to expand outward, and astronomers believe that it only lasts for a few hundred million years before it begins disintegrating. Eventually only the bright galaxy core will remain.

In 2004, astronomers released an image of the ring galaxy AM 0644-741 to celebrate 14 years of service by the Hubble Space Telescope.

We have written many articles about galaxies for Universe Today. Here’s an article about a ring galaxy imaged by Hubble.

If you’d like more info on galaxies, check out Hubblesite’s News Releases on Galaxies, and here’s NASA’s Science Page on Galaxies.

We have also recorded an episode of Astronomy Cast about galaxies – Episode 97: Galaxies.

May 11, 2009December 24, 2015 by Fraser Cain

Comet Galaxy

Galaxy cluster Abell 2667. Image credit: Hubble

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The “Comet Galaxy” is actually just one galaxy located in a distant galaxy cluster known as Abell 2667, located about 3.2 billion light-years away. A recent photograph captured by the Hubble Space Telescope showed this galaxy being torn apart into a comet shape by the intense gravity of galaxy cluster – and that’s how it got the nickname as the Comet Galaxy.

The observation of the Comet Galaxy and the rest of the galaxies in Abell 2667 helped astronomers understand why many galaxies are “gas poor”. Our own Milky Way has tremendous stores of gas and dust which are used for star formation. But other galaxies out there have very little gas which can be used for star formation.

The image of the Comet Galaxy by Hubble helped show that huge gravitational interactions between galaxies in massive clusters cause tremendous damage to the structure of a galaxy, and the amount of gas they have. Galaxies near the center of clusters experience the most damage of all, which galaxies at the outskirts are relatively unharmed. The galaxy collisions can distort the shape of galaxies, and even fling out “homeless stars” into intergalactic space.

Even though the Comet Galaxy’s mass is slightly greater than the Milky Way, it will lose all its gas and dust, and so not be able to generate stars later in life. It will become a gas-poor galaxy with an old population of red stars.

Because the Comet Galaxy is 3.2 billion light-years away, it can only really be seen with the Hubble Space Telescope. Even a powerful backyard telescope wouldn’t be able to locate it.

We have written many articles about galaxies for Universe Today. Here’s a news release from the Hubble Space Telescope about the Comet Galaxy.

If you’d like more info on galaxies, check out Hubblesite’s News Releases on Galaxies, and here’s NASA’s Science Page on Galaxies.

We have also recorded an episode of Astronomy Cast about galaxies – Episode 97: Galaxies.

May 11, 2009December 24, 2015 by Anne Minard

Unusual Cargo Headed to Hubble: A Basketball?

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Most people know Edwin Hubble as a famed astronomer, but he also starred as a forward on the University of Chicago Maroons’ Big Ten champion basketball teams of 1907–08 and 1908–09.

And as fellow Chicago alumnus John Grunsfeld has prepared for his fifth space shuttle flight since 1995, he’s been pondered how best to deflate a century-old ball that Hubble had tossed around in a 1909 victory against Indiana University.

The challenge: Find a way to compactly stow the old pigskin, which to everyone’s surprise lacks an air valve, aboard the space shuttle Atlantis for its upcoming launch.

The problem unfolded last summer in a series of e-mails between Grunsfeld and Michael Turner, a University of Chicago astronomy and astrophysics professor.

“It’s a cosmic mystery as to how the ball was filled, and now for me how to drain it,” Grunsfeld told Turner, who had borrowed the basketball from the university’s athletics program for its orbital flight. Grunsfeld plans to return the basketball personally to the University after the mission, when it will go on display.

“We couldn’t find a valve to deflate it, so we will leave it to the rocket scientists to figure out how to flatten it,” Turner told Grunsfeld. It presented another challenge of the kind that Grunsfeld relishes, but would never have anticipated as an astronaut.

Five weeks before scheduled launch, Grunsfeld punctured the basketball with a hypodermic needle. “Nothing happened, no air hissing out, or any air transfer at all as I compressed the ball,” he said. Grunsfeld assumed that he had punctured the pigskin, but not the underlying air bladder. And yet more punctures with different needles in different locations also failed to deflate the ball.

Finally, with the University’s permission, Grunsfeld resorted to cutting a small incision into the ball. “To my astonishment, I discovered that there is no bladder, and no pressurized air. The basketball was filled with an organic fiber packing,” he said.

Grunsfeld plans to reshape the ball while in orbit and gently pass it around to crewmates during a photo-op. The moment should provide a memorable, light-hearted counterpoint to his usual orbital workload of marathon spacewalks and Hubble Telescope repairs.

Source: Steve Koppes, University of Chicago

May 11, 2009December 24, 2015 by Anne Minard

Milky Way Dwarf Galaxies Thwart Newtonian Gravity?

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Here at Universe Today, the subject of Newtonian gravity always seems to lead to vigorous debate. Now, there’s new research to stoke it.

Manuel Metz, and astrophysicist at the German Aero-space Center, and his colleagues say dwarf galaxies in the Milky Way are arranged in a way that precludes the existence of dark matter — but also depends on it.

“Maybe Newton was indeed wrong,” said Pavel Kroupa, an astronomer at Bonn University. “Although his theory does, in fact, describe the everyday effects of gravity on Earth, things we can see and measure, it is conceivable that we have completely failed to comprehend the actual physics underlying the force of gravity.”

As modern cosmologists rely more and more on the ominous “dark matter” to explain otherwise inexplicable observations, much effort has gone into the detection of this mysterious substance in the last two decades, yet no direct proof could be found that it actually exists. Even if it does exist, dark matter would be unable to reconcile all the current discrepancies between actual measurements and predictions based on theoretical models. Hence the number of physicists questioning the existence of dark matter has been increasing for some time now. Competing theories of gravitation have already been developed which are independent of this construction. Their only problem is that they conflict with Newton’s theory of gravitation.

In two new studies, Metz and his team have examined so-called “satellite galaxies.” This term is used for dwarf galaxy companions of the Milky Way, some of which contain only a few thousand stars. According to the best cosmological models, they exist presumably in hundreds around most of the major galaxies. Up to now, however, only 30 such satellites have been observed around the Milky Way, a discrepancy in numbers which is commonly attributed to the fact that the light emitted from the majority of satellite galaxies is so faint they remain invisible.

A detailed study of these stellar agglomerates has revealed some astonishing phenomena: “First of all, there is something unusual about their distribution,” Kroupa said, “the satellites should be uniformly arranged around their mother galaxy, but this is not what we found.” More precisely, all classical satellites of the Milky Way – the eleven brightest dwarf galaxies – lie more or less in the same plane, they are forming some sort of a disc in the sky. The research team has also been able to show that most of these satellite galaxies rotate in the same direction around the Milky Way, like the planets revolve around the Sun.

The physicists believe that this phenomenon can only be explained if the satellites were created a long time ago through collisions between younger galaxies.

“The fragments produced by such an event can form rotating dwarf galaxies,” Metz said. But there is an interesting catch to this crash theory, “theoretical calculations tell us that the satellites created cannot contain any dark matter.” This assumption, however, stands in contradiction to another observation. “The stars in the satellites we have observed are moving much faster than predicted by the Gravitational Law. If classical physics holds this can only be attributed to the presence of dark matter.”

Or one must assume that some basic fundamental principles of physics have hitherto been incorrectly understood. “The only solution would be to reject Newton’s classical theory of gravitation,” adds Kroupa. “We probably live in a non-Newton universe. If this is true, then our observations could be explained without dark matter.” Such approaches are finding support amongst other research teams in Europe, too.

It would not be the first time that Newton’s theory of gravitation had to be modified over the past hundred years. This became necessary in three special cases: when high velocities are involved (through the Special Theory of Relativity), in the proximity of large masses (through the theory of General Relativity), and on sub-atomic scales (through quantum mechanics).

Source: Eurekalert. The relevant papers are available here and here.

May 10, 2009December 24, 2015 by Tammy Plotner

Lunatic Fringe – Stereo Moon by Jukka Metsavainio

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“I was lying in a burned out basement… With the Full Moon in my eyes…” Hey, welcome to my world. You, know, the Full Moon has been credited to many things over the years… werewolves, disasters, fertility, accidents and even crime, suicide and mental illness. Farmers plant their crops by lunar phases and (strangely enough) I’ve even heard tale that some brokers buy and sell stocks according to phases of the Moon. While it’s more myth than fact that seeing Selene in full light has an effect on our human behavior, one thing is for certain… There’s nothing like the details you can glimpse on this distant, barren, rocky orb. Chances are, if you’re seeing two pictures, then you’re about to embark on another stereo journey thanks to the magic of Jukka Metsavaino. Are you ready to take a quarter of a million mile journey? Then let’s go…

As always, whenever we present a dimensional visualization it is done in two fashions. The first is called “Parallel Vision” and it is much like a magic eye puzzle. When you open the full size image and your eyes are the correct distance from the screen, the images will seem to merge and create a 3D effect. However, for some folks, this doesn’t work well – so Jukka has also created the “Cross Version”, where you simply cross your eyes and the images will merge, creating a central image which appears 3D. For some folks, this won’t work either… But I hope it does for you, because this image blew me away!

At 4:01 a.m. Universal Time on May 9, the Moon was officially considered “full” – the point in the lunar cycle when the Moon exactly opposes the Sun. If you wish to be technical, you could say Full Moon occurs when the geocentric apparent (ecliptic) longitudes of the Sun and Moon differ by 180 degrees. Perhaps a little more colorfully you could just say it was fully illuminated. But, no matter how you say it, the truth is that lunar effects don’t really impact human behavior, except for perhaps sparking a relationship. After all, what’s a good romance without a Full Moon?

The reality check is almost everything you hear associated with the Full Moon is myth that has been perpetuated by folklore and the media. Studies have proved that hormones don’t run any higher and babies aren’t born more frequently at this time. Women aren’t any more fertile and the only reason that more accidents and catastrophes seem to occur when our nearest astronomical neighbor is fully lit is simply because it’s more noticeable – and thereby more memorable. And when you see a Full Moon in a telescope and it looks like the image above? It will live in your memory forever!

Go on… Enjoy it for what it is – and enjoy some of the fun that myth and even astrology can give to a very normal function of our solar system. It’s “Truth or Dare Moon” when it happens in the constellation of Scorpio. In folklore the May Full Moon is called the Hare or Flower Moon… or even the Milk Moon, Dragon Moon, Planting Moon, Panther Moon, Bright Moon, Grass Moon and Worm Moon. According to the Farmer’s Almanac, it’s a favorable time of the Moon to plant beans, beets, cucumbers and potatoes – but not to go fishing. Try astronomy instead!

“Lunatic fringe… I know you’re out there.”

Many thanks to JP Metsavainio of Northern Galactic for his magical personal image and allowing us this incredible look at what we so often take for granted!

May 10, 2009December 24, 2015 by Nancy Atkinson

Final Pretty Picture for Hubble Camera

K 4-55 by the WFPC2 on Hubble. Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)

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Last week we looked back at some of the greatest images and discoveries produced by the Hubble Space Telescope’s Wide Field Planetary Camera 2, the workhorse optical camera that will be replaced with the new and improved WFPC3 during the Hubble servicing mission this week. Now, in tribute to the legacy of WFPC2, the telescope’s science team has released this image as the camera’s final “pretty picture,” a planetary nebula is known as Kohoutek 4-55 (or K 4-55). This image is the last hurrah for the camera that has provided outstanding science and spectacular images of the cosmos.

K 4-55 is nearly 4,600 light-years away in the constellation Cygnus. It is one of a series of planetary nebulae that were named after their discoverer, Czech astronomer Lubos Kohoutek. A planetary nebula contains the outer layers of a red giant star that were expelled into interstellar space when the star was in the late stages of its life. Ultraviolet radiation emitted from the remaining hot core of the star ionizes the ejected gas shells, causing them to glow.

In the specific case of K 4-55, a bright inner ring is surrounded by a bipolar structure. The entire system is then surrounded by a faint red halo, seen in the emission by nitrogen gas. This multi-shell structure is fairly uncommon in planetary nebulae.

The colors represent the makeup of the various emission clouds in the nebula: red represents nitrogen, green represents hydrogen, and blue represents oxygen.
This Hubble image was taken by the Wide Field and Planetary Camera 2 on May 4, 2009.

The scientific and inspirational legacy of the camera will be felt by astronomers and the public alike, for as long as the story of the Hubble Space Telescope is told.

Source: HubbleSite