Globular Clusters – Abode for Life?

The cosmos holds many wondrous things to capture our attention, but to me, the site of a globular cluster is just mesmerizing. These bejeweled orbs can contain tens of thousands to millions of stars in a sphere that can be about 100 light-years (ly) across. (Compare this with our Milky Way spiral galaxy that is approximately 100,000 ly across and contains on the order of 300 billion stars.) There are close to 150 globular clusters orbiting our galaxy, which is not unique; other galaxies have thousands or more in orbit about them.

The globular cluster Omega Centauri, visible from the Southern Hemisphere

Image credit: Joaquin Polleri & Ezequiel Etcheverry (Observatorio Panameño en San Pedro de Atacama)

Globular clusters are made up of very old stars, on the order of 10-13 billion years old. Note that the current estimate for the age of the Universe is about 13.8 billion years old, so these stars are ancient, especially when you compare them to our Sun, which is around 4.5 billion years old. The stars that comprise a cluster are typically smaller, cooler dwarf stars designated as M-class that burn their fuel very slowly giving them their longer lifetime. The larger, hotter stars burned themselves out long ago in brilliant supernovae, peppering the cluster with heavier elements necessary for rocky planet formation. Because these stars are so old, planets that may form in their habitable zones have a greater chance of developing life. But, being in a globular cluster brings its own hazards, which would be a detriment to the evolution of advanced life.  Check out the article by astronomers William Harris and Jeremy Webb, “Life Inside a Globular Cluster“, which discusses some of the potential hazards of living in a globular cluster. (The link will download a pdf of the article.)

The very nature of the cluster, with its large number of stars so close together presents the opportunity for neighboring stars to disrupt the formation of planets or even steal planets from each other. Planets may also be ejected from a stable system by the gravitational influence of a passing star and follow their own path through the cluster. This is not to say that there would not be planets in stable orbits around stars in the cluster, although to date, no planets have been located in a globular cluster. The cluster itself makes it very difficult for us to detect planets orbiting its stars. Take a look at a previous post “Stars in Motion” which has a video showing the somewhat chaotic motion of stars in a globular cluster. It’s not the well ordered system one might intuitively expect from a gigantic ball of stars.

To get a perspective on how dense a cluster is, consider that our nearest star, Proxima Centauri, which is 4.2 ly from us. If you were to map out a sphere at the center of a globular cluster with a radius of 4.2 ly it would contain on the order of 10,000 stars instead of two! These stars would be less than a light-year apart.

A paper was recently published, “Globular Clusters as Cradles of Live and Advanced Civilizations” by Dr. R. DiStefano et al, which discusses the possibilities of planets forming around stars in a globular cluster and surviving long enough for life to form and flourish. But, this is conditional on the planets forming around stars that are located in a “sweet spot” in the cluster; that is, far enough apart that they don’t interfere with each other. Planets that form in the habitable zones of these cooler stars would be less prone to having their orbits disrupted by a passing star because these zones are close to these less massive, cooler stars.

Ringed gas giant with habitable moon on the periphery of a globular cluster. (Click for a larger image.)

A benefit of the stars being in such close proximity is that it makes the possibility of traveling to or communicating with another civilization so much more practical and if advanced life formed, probable.  Also, the high concentration of stars means that planets that have been ejected and not captured by another star may still receive enough light continue to nurture life, especially if the planets retain or generate enough heat to keep water liquid, even if under a layer of ice.

All of this makes me wonder what it would be like to view the cosmos from inside a cluster or just outside of a cluster. The image below represents a possible view of a planet inside the cluster, some distance from the center. The ambient light from all the stars would make nighttime about as bright as dusk/dawn on our planet. Consequently, the beings populating this planet might have a great understanding of the stars around them, but their view of the universe outside of the cluster would be greatly hampered by this collection of stars.

View from inside a globular cluster. (Click for a larger image.)

Check out the very interesting short story by Issac Asimov, “Nightfall”, which is about a civilization that evolved in a globular cluster on a planet with the six suns. They experience constant daylight except once every two thousand and forty-nine years when five of the stars align on one side of the planet and the sixth is eclipsed by a moon unveiling nighttime and all the wonders of the night sky, which they are very unprepared for.

Whether globular clusters are abodes for life or not will not be answered soon. It’s just one more challenge for astronomers to unravel as they sharpen their skills in exploring our amazing cosmos.

Till next time,

RC Davison

Lithium, Stars and Planets

On Earth, the element lithium has certain medicinal properties when applied to conditions like depression and bipolar disorder, and it is extensively used in the battery technology powering most of our portable electronics. In stars, the amount of lithium present is an indicator of the age of a star.

The older the star is, the lower the concentration of lithium measured in the photosphere – the part of the star that we can see. Typically as a star ages, lithium is moved through convective motion deeper into the star where the temperatures are higher and the element is consumed. When astronomers find a star that shows a higher than normal lithium content for its age, eyebrows get raised and heads get scratched.

After the big bang, the Universe (by mass) was about 75% hydrogen, 25% helium and extremely small trace amounts of lithium, all the other elements we have today have been synthesized in stars as they move through their normal life cycle.  Elements heavier than iron are produced when the more massive stars explode as supernova.  The first stars that formed after the big bang (called Population III stars) reflected the amounts of hydrogen, helium and lithium originally present.  Second generation stars (Population II) contained higher levels of the elements heavier than lithium thanks to the first generation enriching the cosmos, but these are considered “metal poor” when compared to Population I stars, like our Sun.  (Astronomers consider any elements heavier than helium to be metals.)

The planets that form around a star contain the primordial elements of the big bang, along with whatever new elements have been seeded in the protoplanetary dust cloud from novae and supernovae. Lithium is preserved in the relatively cold planets as they condense and solidify. If a planet containing lithium is pulled into its parent star, it will disintegrate, spreading its contents though out the star’s atmosphere. This mechanism can explain how a star can have a higher than normal lithium content for its age.  But, this process is transitory.  Eventually, the lithium will be processed by the star.

There have been two recent observations of stars that show higher than normal amounts of lithium:

One is associated with a red giant star (BD+48 740) that is suspected to have at least one planet orbiting it in a highly eccentric orbit. Dr. Alex Wolszczan, professor of Astronomy and Astrophysics at Penn State University, has led the team which discovered this youthful red giant. Evidence indicates that the star has a massive planet in a very elliptical orbit, which is unusual but can be attributed to gravitational interactions between planets in the solar system. This interaction may have contributed to another planet moving too close to the parent star and being engulfed as the red giant swells with age, giving rise to the higher than normal lithium content.

Red Giant engulfs one of its planets. (Image courtesy of NASA)

The other observation is of a star (#37934) in the globular cluster NGC 6121, also known as Messier 4 or M4.  The ESO (European Southern Observatory) has released an image of M4 and discusses the surprising discovery.

Globular cluster M4, NGC 6121 (Image courtesy of the European Southern Observatory)

This star peculiar in that it is exhibiting a much higher than normal level of lithium for the ancient stars (Population II) that typically make up globular clusters. In the paper presented on this observation the authors present two scenarios that may explain this star’s unusual concentration of lithium.  The first is that the star formed with a higher than normal amount of the element  – i.e. it was polluted by its environment.  The other thought is that the star, for some unknown reason, hasn’t processed the lithium like the rest of the stars in the cluster.  Both ideas are up for debate as there isn’t enough evidence to prove either one correct.

But, could this star have sacrificed one of its planets for a brief period of youthful lithium enrichment like BD+48 740? (This assumes that it has or had planets orbiting it.)

Star in M4 exhibiting higher than normal lithium levels. (Image courtesy of the European Southern Observatory)

Perhaps the discovery by Dr. Wolszczan and his team shows a stellar process that is more common than thought.  If one considers the high number of planets being discovered by Kepler, which is leading astronomers to predict even greater number of stars with orbiting planets, this idea may be even more plausible.

Another case of the cosmos leading us down a rabbit hole just like Alice in Wonderland – the more we look, the more we see and the more questions we raise.  The Universe just gets curiouser and curiouser!

Link to published papers:

BD+48 740 – Li overabundant giant star with a planet. A case of recent engulfment?

Lithium and sodium in the globular cluster M4. Detection of a Li-rich dwarf star: preservation or pollution?

Till next time,

RC Davison

Galaxies in Collision

In the vastness of the cosmos it seems amazing that objects run into each other, but they do. The pervasiveness of gravity has dominated and shaped the Universe as we see it today, from simple planets and solar systems to vast galactic clusters containing thousands of galaxies bound together. Galaxies collide, and galactic collisions create some of the most beautiful structures we’ve seen in our search of the cosmos.

Here we have The Mice:

Two galaxies colliding, known as The Mice - NGC 4676. Image Courtesy of NASA/Hubble Space Telescope

The Exclamation Point:

Arp 302 - Two galaxies about to collide - Image courtesy X-ray NASA/CXC/IfA/D.Sanders et al; Optical NASA/STScI/NRAO/A.Evans et al

Sometimes what appears to be a collision about to happen is really a case of one’s perspective, as can be seen in this image from the Hubble Space Telescope of NGC 3314.

Colliding galaxies? Not really. Image courtesy of NASA/Hubble Space Telescope

The galaxy that we see almost face-on – NGC 3314a is in the foreground and is tens of millions of light years from the background galaxy NGC 3314b. These two galaxies will not become another statistic in the annals of galactic collisions. But, the same can not be said for our own Milky Way galaxy and the Andromeda galaxy (M31).

In the next four million years or so, these two galaxies will begin to become one through a graceful pas de deux that will take millions of years and result in what theory predicts will be a large elliptical galaxy. This information, along with some amazing simulations and illustrations can be found at the Hubble Space Telescope’s site.

Here’s a graphic illustrating the collision showing the paths of the two galaxies along with another galaxy in our Local Group, Triangulum (M33):

Illustration of the Milky Way and Andromeda galaxies ultimate demise. - Image courtesy of NASA/Hubble Space Telescope

In this artist’s conception, the collision is seen from the perspective of an observer on Earth.

Illustration of the Andromeda galaxy's approach - Image courtesy of NASA/Hubble Space Telescope

The last few frames shows how Andromeda dominates the night sky and effectively blocks our view of that portion of the Universe. Future astronomers will not be able to appreciate the night sky as we are able to today.  But, who knows if humans will still be observing the Universe by the time this event takes place.

Looking at these images I can’t help but wonder about the alien astronomers living in the Triangulum galaxy. What a spectacular view they have of this doomed pair of galaxies. I wonder if they have mapped out the motions of these island universes (as they were once known) and understand that they will eventually collide. And, even more mind-boggling: Are they looking at us and wondering if someone is looking back?

Till next time,

RC Davison

 

Andromeda – Beyond the Blue

Hopefully we are all aware of the fact that ultraviolet rays from the Sun are bad for our skin.  The reason they are hazardous is because of the high energy that that they possess, which allows them to penetrate our skin and damage the cells internally. UV is a small part of our Sun’s emissions but UV radiation is a major component of the energy emitted by very hot, massive stars, as can be seen in the image below from NASA’s Galex (Galaxy Evolution Explorer) satellite.

Andromeda Galaxy in UV - Image courtesy of NASA

These stars that line the arms of the Andromeda galaxy are the result of dust and gas that form the structure of the arms and consequently, the birthing place of new stars.  Blue giants have very high surface temperatures ranging from 10,000 to more than 40,000 degrees Kelvin.  The more massive the star, the hotter it is and the more it will radiate in the ultraviolet.  But, running hot and massive comes with a cost.  These blue giants will burn out in supernovae in a few tens of million of years. (A very short time – astronomically speaking!)  Compare this with our Sun, which has a surface temperature of about 6000 degrees Kelvin and will be around for at least 10 billion years.

Below you can see Andromeda in a Hubble image in the optical spectrum fading to the ultraviolet image from Galex.  It’s easy to see that these high-powered stars reside in the dusty arms of the galaxy.  In a few million years the Milky Way Galaxy will have a ring-side seat to view these blue giants as they spectacularly end their lives!

Andromeda from Hubble in visual and UV from Galex

For more on the Andromeda galaxy take a look at an earlier post to see Andromeda in a different light: The Many Faces of Andromeda.

Till next time,

RC Davison

Dwarf Galaxy NGC 2366 and Beyond!

A smudge in the night sky can contain many wonders!

Ground-based, wide-field view of NGC 2366 from Digital Sky Survey 2 - Image courtesy of NASA

The blue streak in the above image is the dwarf galaxy NGC 2366.  It is about 10 million lightyears distant and located in the constellation Camelopardalis (the Giraffe), which is visible in the northern hemisphere.  Barely visible to the bottom right of the blue smudge is a bright spot, which is an active star-forming nebula, NGC 2363 contained within the dwarf galaxy.  In the image below you can see the nebula shining from the light of the hot blue stars that are forming in the upper right part of the galaxy.

Hubble view of NGC 2366 - Image courtesy of the NASA/ESA Hubble Space Telescope

Zooming in on the nebula in another Hubble image below, one can see the collection of bright stars embedded in the nebula.  Of particular note is the very bright star that appears at the tip of the “hook” of the nebula.  This massive star is known as a Luminous Blue Variable (LBV), which is about 30 to 60 times as massive as the Sun.  This is a very rare type of variable and very unstable.  The image captured the star during an erupting phase.  Another, more famous star of this type is the giant, Eta Carinae, which is anticipated to turn into a supernova in the near future (astronomically speaking).

NGC 2363 - Star forming nebula in the dwarf galaxy NGC 2366 - Image courtesy of NASA

When you look closely at the image of NGC 2366 you will see many “nebulous” regions within it.  They are actually very distant galaxies that are visible through the veil of the dwarf galaxy.  I’ve highlighted some of the more prominent galaxies that can be found in the image below.

Galaxies beyond NGC 2366 - Base Image courtesy of NASA/ESA Hubble Space Telescope

Here is a composite of some of the major galaxies hiding behind this dwarf galaxy.

Galaxies behind the dwarf galaxy NGC 2366

NGC 2366 is just another example of what wonders are hidden within the smallest parts of the night sky and what amazing things are awaiting discovery.

Till next time,

RC Davison

Resource: Hubble Space Telescope NASA/ESA Hubble Observes a Dwarf Galaxy with a Bright Nebula

Unique Views of the Cosmos

Two items of interest popped up last week:

First:  The European Space Agency posted a very nice video showing the Andromeda Galaxy in light from X-rays to gamma rays.  About a third of the way into the video, one can see variable stars pulsing and other stars flashing as they go nova, thanks to the view from the XMM-Newton X-ray telescope. Check out “Andromeda’s coat of many colours“.  (Check out the post on 6, January 2011 under the galaxy category for more information about Andromeda.)

Andromeda Galaxy (M31) iImage courtesy of Tony Hallas and APOD.NASA.Gov

Second:  An image posted on the Astronomy Picture of the Day site by Juergen Michelbergershows in very unique detail how stars and planets are affected by Earth’s atmosphere.  Or, more appropriately, why stars twinkle and planets don’t.

The star Regulas (left) and Mars (right): Image by Juergen Michelberger

The star, being much further away from Earth than the planet Mars, presents an image that is much smaller in diameter than Mars.  This smaller point of light is affected by the variations of the Earth’s atmosphere due to temperature and moisture much more so than the larger source of light from the planet.  Consequently, the star’s image is randomly refracted, causing it to vary in color and brightness, while Mars shines on steadily over the ten second exposure.  The intricate image is due the camera being swung about.  Check out the link to APOD above for more information about this unique image.

Till next time,

RC Davison

Galaxies Dancing the Tango

Interacting galaxies come in all shapes and sizes.  This pair, known as Arp 237 or UGC-1810 and UGC-1813 bear a striking resemblance to a flower – a rose as stated on the Hubble siteis even more precise.

Galaxies Colliding UGC-1810 and 1813: Image Courtesy of Hubble Site

 (Link to larger images)

     The blue “icing”at the top of the image are hot blue stars that have formed in the wake of the collision.  You can also see a region of new star formation in the center of the smaller galaxy, also most likely due to the collision.

     But, there are jewels strewn all about in this image: A small blue galaxy to the left of the larger UGC-1810 and a red spiral galaxy visible between its arms to the lower right.

         Blue Galaxy     Red Galaxy

   This clip will show you where the galaxies are and zoom in to them.  But, if you can, download the largest image possible, zoom in and explore this beautiful image.

    It is also noteworthy that this image commemorates Hubble’s 21st anniversary of operation in space.  It’s hard to imagine that is has been that long!

     A note about housekeeping on the site.  I’ve categorized the blog posts so it will be easier if you are looking for a particular post to search by category.  The categories used are listed at the bottom of the post and you can click on them to sort the blog.  They are also listed on the right side of the web page.

  • Astronomy
  • Cosmology
  • Galaxy
  • Humans in Space
  • Orbital Maneuvers
  • Solar System

Hopefully this will be of use to you in the future.

Till next time,

RC Davison

A Gossamer Galaxy – NGC 4921

There are jewels in the night sky and some of them are more fanciful than others. The spiral galaxy NGC 4921 is a case in point. Please click on the following links in the article for much higher resolution images. (Click for a larger image.)

NGC 4921 Image Courtesy of Hubble/ESA

This beautiful barred-spiral galaxy resembles more a ghostly cosmic jelly fish than the typical spiral galaxy you may think of like the Whirlpool galaxy (M101) below:

Whirlpool Galaxy - Image Courtesy of Adam Block, Mt. Lemmon SkyCenter, U Arizona

You’ll notice immediately that NGC 4921 is missing the well defined spiral arms seen in the Whirlpool. There is structure there, but it is much more subtle.  You do see a dark swirl of dust around the core, accented with bright blue stars that are forming along this band.  And, you can see the bar that extends across the nucleus of the galaxy as well as some spiral structure to the arms.

To me, what is most remarkable about this galaxy is that the white gossamer cloud is not dust but stars – billions and billions of unresolved stars spread very uniformly around the galaxy.  In a well defined spiral galaxy we don’t get the same impression of the vast number of stars contained within because they are clumped together in the arms.  NGC 4921 and the Whirlpool galaxies are roughly the same size (about 200,000 lightyears verses 175,000 lightyears across), so comparing the two galaxies gives a good sense of how many stars are condensed into the arms.  It is interesting that this type of galaxy is termed an “anaemic spiral” because of the uniform distribution of stars.

The galaxy is located about 320 million lightyears away in the galaxy cluster known as the Coma Cluster or alternatively Abell 1656 in the constellation Coma Berenices.  If you look closely at the image you will see thousands of galaxies scattered about NGC 4921 and even behind the nebulous galaxy.  Some are part of the Coma Cluster, while others extend much further beyond it.  This annotated image below (Click for a larger image.) shows highlights some of the details contained in this amazing image.

NGC 4921 Annotated Image Courtesy of Hubble/ESA

     Check out the Hubble website for more information, images and several short videos that will give you more in-depth information about this beautiful jewel of the night sky.   Enjoy the wonders of the Cosmos!

Till next time,

RC Davison

Many Faces of Andromeda

The Andromeda galaxy is one of my favorite galaxies, so the latest images from the European Space Agency (ESA) are a real treat.  Using the Hershel observatory to take Andromeda’s portrait in the infrared and the XMM-Newton X-ray observatory to capture the galaxy’s image in the high energy spectrum, ESA has produced a composite image that shows the star birthing and dying regions of the galaxy in the highest resolution to date.

Multispectral views of Andromeda from ESA's Hershel and Newton

      The top right image show the galaxy in the infrared as taken by Hershel.  This shows the regions of the galaxy where there are concentrations of dust that harbor the development and birth of stars.  The image at the lower right shows the regions hot with X-rays, which is indicative of gas being heated to extremely high temperatures from the shockwaves produced when stars meet their end as novas and supernovas. X-rays can also be generated as one star pulls material from another in a binary pair.  This gas is heated to high temperatures as it is accelerated in its fall to the parasite star.

     The image also shows a high concentration of X-rays at the center of the galaxy, which is to be expected because of the high density of stars there and the resident supermassive black hole that resides at the core of the galaxy. If you look closely at the X-ray image there appears to be a bubble surrounding the core of the galaxy.  Possibly a shockwave propagating outward from the core, indicating a more active period of the galaxy’s massive black hole. Be sure to check the links to see the all the detail in these great high-resolution images.

     Take a look at ESA’s website for more information on these new images of Andromeda.

Till next time,

RC Davison

Speaking of Galaxies…

In the last post (It’s Full of Galaxies) we saw an infrared image from the Herschel space telescope looking at a tiny piece of the cosmos revealing thousands of galaxies 10 – 12 billion light-years from us.  The image below is also an infrared image, but it is a view of millions of galaxies as taken by the 2MASS (Two Micron All Sky Survey) looking across the night sky.

2MASS View of the Night Sky

      The blue band in the image comes from the stars in our own galaxy.  Note that the distribution of galaxies is not uniform, as one might expect but there are clusters, strings and webs of galaxies.  These structures are remnants of the big bang and the gravitational attraction between matter and the mysterious dark matter.  Think about this:  All of the matter we can see and account for in the Universe only adds up to about 4-5% of the total mass of the Universe!

     The  2MASS survey was conducted using two 1.3 meter telescopes, one in Arizona and the other in Chile, imaging the sky at 3 separate frequencies in the near infrared.  Imagine what this would look like if we were able to use telescopes in space that are above the filtering effects of our atmosphere in the infrared.

      Check these links for more information and a larger image.

Till next time,

RC Davison