Galaxies - Introduction

A galaxy is an organized system of hundreds of millions to thousands of billions of stars, sometimes mixed with interstellar gas and dust.

Our sun and solar system are part of the Milky Way galaxy.

Galaxies can be seen in every direction in space, each with billions of stars. Galaxies often appear to be distinct but fuzzy patches of light.

Charles Messier (1730-1817) cataloged more than 100 fuzzy celestial objects, sometimes called Messier objects, and named M1 to M110.

Dreyer compiled the New General Catalog of nearly 8000 objects around 1900. Most of these fuzzy objects are planetary nebulae and star clusters that are part of our galaxy, but extragalactic objects (or galaxies) were also included.

Nearest neighboring large galaxy = Andromeda Galaxy (M31). The relatively "nearby" Andromeda Galaxy (M31) is about 2.2 million light years away.

The Local Group is a group of our nearest galaxy neighbors, held together by their mutual gravitational attraction. About 20 galaxies are in this area.

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Classification of Galaxies

In the 1920's, Hubble devised a classification of galaxies:

1. Spiral galaxies (30%)
2. Elliptical galaxies (most common - 60%)
3. Lenticular galaxies (transitional orms between sprial and elliptical galaxies)
4. Irregular galaxies (10%)

Spiral galaxies are flat disks with a nuclear bulge, a halo of old stars, and spiral arms with young stars. Some have a bar-shaped concentration of stars in the center (barred spirals). Arms emerge fromt he ends of the bar. Dust is readily visible as dark streaks. The Milky Way galaxy is a spiral galaxy.

Globular clusters encircle spiral galaxies. Elliptical galaxies are spheroidal in shape (elliptical in two dimensions). Old stars are dominant. There is no prominent internal structure. They are circled by a halo of globular clusters. Little or no gas and dust are present. Almost all has been converted into stars.

Irregular galaxies are ot disk-like or spheroidal and have no nucleus. They have a chaotic, irregular appearance. Some have bars, but no arms. Sites of active star formation with young stars and luminous gas clouds. Some very old stars are present in globular clusters.

Examples of irregular galaxies are the Small Magellanic Cloud and the Large Magellanic Cloud.

universe

Solar Activity Heats Up

August 28 saw a major solar flare erupting from a complex sunspot group crossing the Sun's southern hemisphere. The intensity of the eruption placed it in the most powerful "X" category. The flare was accompanied by a coronal mass ejection (CME) which was clocked at 600 km/hr as it headed past the Earth. This CME passed south of Earth's orbital plane and did not cause any major effects here. However, CMEs that collide directly with the Earth can excite geomagnetic storms, which have been linked to satellite communication failures. In extreme cases, such storms can induce electric currents in the earth and oceans that can damage electric power transmission equipment. Scientists expect to see solar flare-ups daily during the solar max, which is expected in mid-2000.

Leaking Earth Could run dry

Researchers from the Tokyo Institute of Technology say that Earth could be dry and barren within a billion years because the oceans are draining into the planet's interior. They have calculated that about 1.12 billion tonnes of water leaks into the Earth each year. Although a lot of water also moves in the other direction, not enough comes to the surface to balance what is lost. The scientists believe that eventually all of it will disappear. They predict that the Earth's surface will look a lot like the surface of the planet Mars where a similar process seems to have taken place. This research was published in the New Scientist magazine. Mir drifts free

Russian space station Mir has gone into "free drift" mode as control passes to a new onboard computer. The free flight is necessary to reduce power consumption so that Mir can survive for months in space before a possible return by cosmonauts. The last crew left on August 27, just 10 days before Mir would have celebrated 10 years of continuous crewing. The new computer keeps the solar panels pointed at the Sun so Mir's batteries remain charged. Russia is expected to make a decision late this year or early next on whether Mir will remain in orbit. The station costs about $250 million a year to operate and while this is not too high in space terms, Russia just doesn't have the money.

Shaking Earth

The centuries-old mystery of why the Earth appears to wobble has been solved. Every 1.2 years, the planet appears to move about its axis by about 20 ft at the North Pole, but since discovering the so-called Chandler Wobble in 1891, scientists had been unable to explain it. Now NASA believes that the cause lies in the Earth's oceans. Fluctuating pressure of water on the ocean bed caused by temperature, salinity and current changes - forces the Earth to move slightly on its axis. Atmospheric fluctuations add to the wobble. The findings were made by analyzing data from the International Earth Rotation Service, set up in Paris in 1988.

Moon Magic

The Moon has always been an object of fantasy as well as research but we still don't know exactly how the Earth got its moon.

According to the 'giant impact theory', proposed in the 1970s, the moon was formed after the Earth was hit by a huge object, as big as Mars.

Using the new model, researchers at the Southwest Research Institute and the University of California at Santa Cruz, created high-resolution simulations to show that an oblique impact by an object with 10 per cent of the mass of Earth could have ejected sufficient iron free material into Earth's orbit to eventually coalesce into the moon, while also leaving the Earth with its present mass and correct initial rotation rate.

The simulation also implies that the moon formed near the very end of Earth's formation, some 4.5 billion years ago. The moon is believed to have played an important role in making the Earth habitable because of the stabilizing effect it had on the tilt of Earth's rotation.

New Solar System Is Like Ours

After 15 years of searching, astronomers say they have found an alien planetary system that reminds them a lot of home. This is the first time planet hunters have detected what they believe is a Jupiter-like gas ball orbiting a star much like our Sun, at a distance that allows for the possibility of an unseen Earth-type planet orbiting in between.

In the last decade and a half, scientists have found more than 90 so-called extra-solar planets around stars outside our solar system. But none of these earlier discoveries has held the same potential to answer an essential question: Might there be other Earths in the universe?

"We have a (planetary) system that is maybe not a sibling of the solar system… it might be more accurately classified as a first cousin," Paul Butler of the Carnegie Institution said on Thursday.

Butler and fellow planet-hunter Geoffrey Marcy of the University of California-Berkeley noted that the newly discovered Jupiter-type planet is the third thought to orbit 55 Cancri, a star in the constellation Cancer that can be seen without telescopes or even binoculars. It is about as old – five billion years or so – and about the same size as our Sun. Aside from it known planets, the new planetary system has a tantalizing gap between the new Jovian discovery and two other big gas planets orbiting very close to the star, Marcy said.

There’s a huge region centered at about Earth-Sun distance, and in that gap… an Earth-mass planet could exist … and such a planet would be stable, " he said. "It could persist there for billions of years, so it’s conceivable that this system has rocky planets like Mars, Venus or Earth and we simply can’t detect them," Marcy said.

Heavy Traffic Heads for Mars

American space agency NASA has outlined ambitious, long-term plans to explore the planet Mars. It says six major missions will take place in little more than 10 years, with Italy and France also participating. At an annual cost estimated at $400 million to $450 million a year for the next five years, the agency will dispatch a combination of orbiting spacecraft and landers to the Red Planet. Then, after 2010, the agency will undertake a mission to bring back samples from Mars. In 1999, NASA lost two Martian missions : the Mars Polar Lander and the Mars Climate Orbiter. The failures were a huge blow and prompted a major review of the way NASA carries through its space operations. The campaign to explore Mars is unparalleled in the history of space exploration. It’s meant to be a robust, flexible, long-term programme that will give the highest chances for success. The new strategy is aimed to answer questions about Mars’ mineralogy, geology and climate history. The idea is to ‘follow the water’ so we may know the answers to far-reaching questions about the red planet humans have asked over the generations: Did life ever arise there, and does life exist there now ?"

Astronomers spot winking baby star

A Sun-like star just out of infancy has winked at astronomers, indicating its eclipse by cosmic dust and rocks, the stuff of which planets like Earth could possibly form, scientists reported on Wednesday.

The star, located in the Unicorn constellation about 2,400 light years from Earth, disappeared from view for regular periods of about 48 days over the past six years. Its disappearance suggested an eclipse, but not a typical one caused by an intervening planet, star or moon.

Only a collection of smaller objects, like dust and rocks, could cause the long eclipse the astronomers saw. Known as KH 15D, the star is only about 3 million years old, a prime age for monitoring by astronomers interested in our solar system's planet-forming past.

"We've monitored thousands of these stars over the years and this is the only that behaves this way," said astronomer William Herbst of Wesleyan University in Connecticut. "Essentially the star winks at us."

The dust that caused the wink is different from the fine interstellar dust that is distributed throughout the cosmos. Herbst said. Its particles are bigger, indicating that it is clumping into what astronomers call a protoplanetary disk - the disk from which planets can form.

"Is there a mass in here that is somehow sculpting the obscuring clouds so that it's producing these rings of material which then circle around the star and alternately block the object? We think that's very possible," Herbst said. There could be two blobs circling the star, or just one, but there is no confirmation as yet of exactly what could be causing this kind of disk to form, said Herbst's colleague Catrina Hamilton.

At just 3 million years old, KH 15D is a cosmic toddler barely out of infancy. By contrast, our solar system is thought to be about 4.5 billion years old. However, some astronomers believe the planets may have begun forming when the Sun was a few million years old.

The disk is forming quite close to the star, closer than the planet Mercury is to the Sun. "The star is ... like the Sun was when it was 3 million years old, so the processes that are going on in this inner disk region, where terrestrial planets would be forming - could be analogous to what was going on with the formation of Earth," Herbst said.

Star crust 10 billion times stronger than steel

BLOOMINGTON, Ind. -- Research by a theoretical physicist at Indiana University shows that the crusts of neutron stars are 10 billion times stronger than steel or any other of the earth's strongest metal alloys.

Charles Horowitz, a professor in the IU College of Arts and Sciences' Department of Physics, came to the conclusion after large-scale molecular dynamics computer simulations were conducted at Indiana University and Los Alamos National Laboratory in New Mexico. The research will appear Friday (May 8) in Physical Review Letters.

Exhibiting extreme gravity while rotating as fast as 700 times per second, neutron stars are massive stars that collapsed once their cores ceased nuclear fusion and energy production. The only things more dense are black holes, as a teaspoonful of neutron star matter would weigh about 100 million tons.

Scientists want to understand the structure of neutron stars, in part, because surface irregularities, or mountains, in the crust could radiate gravitational waves and in turn may create ripples in space-time. Understanding how high a mountain might become before collapsing from the neutron star's gravity, or estimating the crust's breaking strain, also has implications for better understanding star quakes or magnetar giant flares.

"We modeled a small region of the neutron star crust by following the individual motions of up to 12 million particles," Horowitz said of the work conducted through IU's Nuclear Theory Center in the Office of the Vice Provost for Research. "We then calculated how the crust deforms and eventually breaks under the extreme weight of a neutron star mountain."

Performed on a large computer cluster at Los Alamos National Laboratory and built upon smaller versions created on special-purpose molecular dynamics computer hardware at IU, the simulations identified a neutron star crust that far exceeded the strength of any material known on earth.

The crust could be so strong as to be able to elicit gravitational waves that could not only limit the spin periods of some stars, but that could also be detected by high-resolution telescopes called interferometers, the modeling found. An online version of the research paper, "The breaking strain of neutron star crust and gravitational waves," can be found at http://arxiv.org/PS_cache/arxiv/pdf/0904/0904.1986v1.pdf.

"The maximum possible size of these mountains depends on the breaking strain of the neutron star crust," Horowitz said. "The large breaking strain that we find should support mountains on rapidly rotating neutron stars large enough to efficiently radiate gravitational waves."

Because of the intense pressure found on neutron stars, structural flaws and impurities that weaken things like rocks and steel are less likely to strain the crystals that form during the nucleosynthesis that occurs to form neutron star crust. Squeezed together by gravitational force, the crust can withstand a breaking strain 10 billion times the pressure it would take to snap steel.

Earlier this year, Horowitz was elected a fellow of the American Physical Society, the preeminent organization of physicists in the United States, for his contribution to research in dense nuclear matter. His most recent work on neutron stars was supported by a grant from the U.S. Department of Energy and through Shared University Research Grants from IBM to IU. Working with Horowitz were Don Berry, a principal systems analyst with the High Performance Applications Group in University Information Technology Services at Indiana University, and Kai Kadau at Los Alamos National Laboratory.

Hubble repair mission

A $70 million instrument designed by the University of Colorado at Boulder to probe the evolution of galaxies, stars and intergalactic matter from its perch on the orbiting Hubble Space Telescope is on schedule for its slated May 11 launch from Kennedy Space Center in Florida aboard NASA's space shuttle Atlantis.

Originally scheduled for launch in 2004, NASA's Hubble Servicing mission has been beset by delays over the years by causes ranging from the Columbia space shuttle accident to mechanical glitches. But CU-Boulder Professor James Green of the Center for Astrophysics and Space Astronomy, principal investigator for $70 million Cosmic Origin Spectrograph, or COS, said from the Kennedy Space Center today things look very good for the launch of Atlantis next Monday at 2:01 p.m. EDT.

""There have been no hiccups this time around and everything is going very smoothly," said Green. We are right on schedule and the team is optimistic about the launch."

The telephone-booth-sized COS, built primarily by CU-Boulder's industrial partner, Ball Aerospace & Technology Corp. of Boulder, should help scientists better understand the "cosmic web" of material believed to permeate the universe, said Green. COS will gather information from ultraviolet light emanating from distant objects, allowing scientists to look back several billion years and reconstruct the physical conditions and evolution of the early universe.

Distant quasars will be used as "flashlights" to track light as it passes through the cosmic web of long, narrow filaments of galaxies and intergalactic gas separated by enormous voids, said Green. Astrophysicists have theorized that a single cosmic web filament may stretch for hundreds of millions of light-years, an astonishing length considering a single light-year is about 5.9 trillion miles.

Light absorbed by material in the web should reveal "fingerprints" of matter like hydrogen, helium and heavier elements, allowing scientists to build up a picture of how the gases are distributed and how matter has changed over time as the universe has aged, Green said.

The spectrograph will break light into its individual components much like a prism, revealing the temperature, density, velocity, distance and chemical composition of galaxies, stars and gas clouds, said Professor Michael Shull of CASA, a co-investigator on COS. The team has chosen hundreds of astronomical targets in all directions of space, which will allow them to build a picture of the way matter is organized in the universe on a grand scale, Shull said.

Shull said one of the earliest COS targets will be a quasar previously looked at by Hubble that is believed to have formed about 5 billion years ago – more than one-third of the way back in time and space to the Big Bang. "This instrument is ten times more sensitive than any previous Hubble ultraviolet instruments, so we are looking forward to studying intergalactic space at this distant epoch in detail."

While matter is thought to have been distributed uniformly throughout space just after the Big Bang, gravity has shaped it into its present filamentary structure known as the cosmic web, said Shull. "Pointing our instrument at hundreds of targets over time will allow us to take a CAT scan of the universe."

COS also will be used to detect young hot stars shrouded in the thick dust clouds they formed in, providing new information on star birth, said CASA Senior Research Associate Cynthia Froning, COS project scientist. Scientists also will point COS at gas surrounding the outer planets of the solar system to glean new clues about planetary evolution.

Green and his COS science team, which is made up of 14 CU-Boulder scientists and engineers and 10 scientists from other institutions, have been allotted 552 orbits of observation time on Hubble. CU-Boulder's CASA is in the process of hiring several dozen postdoctoral researchers, graduate students and undergraduates to work on the project in the coming years, Green said.

The cosmos is green

For the first time, researchers have observed a singular cosmic act of rebirth: the transformation of an ordinary, slow-rotating pulsar into a superfast millisecond pulsar with an almost infinitely extended lifespan.

The discovery was made during a large radio sky survey by an international team of astrophysicists at McGill University, the University of British Columbia (UBC), West Virginia University, the U.S. National Radio Astronomy Observatory (NRAO) and several other institutions in the United States, the Netherlands and Australia.

The sky survey used the Robert C. Byrd radio telescope at Green Bank, West Virginia to observe nearly a third of the celestial sphere. The team's results will be published online by the journal Science on May 21.

The discovery was made by astrophysics PhD candidate Anne Archibald and her supervisor, Prof. Victoria Kaspi of the McGill Pulsar Group. "This survey has found many new pulsars, but this one is truly special -- it is a very freshly 'recycled' pulsar that is emerging straight from the recycling plant." said Archibald. The McGill researchers worked with Asst. Prof. Ingrid Stairs of UBC and Scott Ransom of NRAO as well as others from the collaboration to carry out more observations of this unusual pulsar.

Pulsars are rapidly rotating, highly magnetized neutron stars, the remnants left after massive stars have exploded as supernovae. Pulsars emit lighthouse-like beams of radio waves that sweep around as the star rotates. Most rotate relatively slowly, ten times a second or less, and their magnetic fields ordinarily slow them down even further over the course of millennia. Millisecond pulsars, however, rotate hundreds of times a second.

"We know normal pulsars typically pulsate in the radio spectrum for one million to ten million years, but eventually they slow down enough to die out," explained Kaspi. "But a few of these old pulsars get 'recycled' into millisecond pulsars. They end up spinning extremely fast, and then they can pulsate forever. How does nature manage to be so green?"

It has long been theorized that millisecond pulsars are created in double-star systems when matter from the companion star falls into the pulsar's gravity well and increases the rotation speed, but until now the process has never been observed directly.

"Imagine a ping-pong ball in the bathtub, and then you take the plug out of the drain," explained Archibald. "All the water swirling around the ping-pong ball suddenly makes it spin a lot faster than when it was just bobbing on the surface.

"We've seen systems that are undergoing spin-up, because when the matter is falling in, the stars get really bright in X-rays and they're easy to see," she added. "But we've never seen radio pulsations from these stars during the process of spin-up. At last we've found a true radio pulsar that shows direct evidence for having just been recycled."

The pulsar found by the survey team was fortuitously observed by an independent, optical research group to have had swirling matter surrounding it roughly a decade ago -- the blink of an eye in astronomical time. That group recorded the observation as puzzling, never dreaming that a full-fledged radio pulsar would emerge.

"In other words, for the first time, we have caught a glimpse at an actual cosmic recycling factory in action," said Ingrid Stairs of UBC, who has been visiting the Australia Telescope National Facility and Swinburne University of Technology this year. "This system gives us an unparalleled cosmic laboratory for studying how millisecond pulsars evolve and get reborn."