milky way Archives

May 30, 2017 by Fraser Cain

What Was Cosmic Inflation? The Quest to Understand the Earliest Universe

The Big Bang. The discovery that the Universe has been expanding for billions of years is one of the biggest revelations in the history of science. In a single moment, the entire Universe popped into existence, and has been expanding ever since.

We know this because of multiple lines of evidence: the cosmic microwave background radiation, the ratio of elements in the Universe, etc. But the most compelling one is just the simple fact that everything is expanding away from everything else. Which means, that if you run the clock backwards, the Universe was once an extremely hot dense region

A billion years after the big bang, hydrogen atoms were mysteriously torn apart into a soup of ions. Credit: NASA/ESA/A. Felid (STScI)).

Let’s go backwards in time, billions of years. The closer you get to the Big Bang, the closer everything was, and the hotter it was. When you reach about 380,000 years after the Big Bang, the entire Universe was so hot that all matter was ionized, with atomic nuclei and electrons buzzing around each other.

Keep going backwards, and the entire Universe was the temperature and density of a star, which fused together the primordial helium and other elements that we see to this day.

Continue to the beginning of time, and there was a point where everything was so hot that atoms themselves couldn’t hold together, breaking into their constituent protons and neutrons. Further back still and even atoms break apart into quarks. And before that, it’s just a big question mark. An infinitely dense Universe cosmologists called the singularity.

When you look out into the Universe in all directions, you see the cosmic microwave background radiation. That’s that point when the Universe cooled down so that light could travel freely through space.

And the temperature of this radiation is almost exactly the same in all directions that you look. There are tiny tiny variations, detectable only by the most sensitive instruments.

Cosmic microwave background seen by Planck. Credit: ESA

When two things are the same temperature, like a spoon in your coffee, it means that those two things have had an opportunity to interact. The coffee transferred heat to the spoon, and now their temperatures have equalized.

When we see this in opposite sides of the Universe, that means that at some point, in the ancient past, those two regions were touching. That spot where the light left 13.8 billion years ago on your left, was once directly touching that spot on your right that also emitted its light 13.8 billion years ago.

This is a great theory, but there’s a problem: The Universe never had time for those opposite regions to touch. For the Universe to have the uniform temperature we see today, it would have needed to spend enough time mixing together. But it didn’t have enough time, in fact, the Universe didn’t have any time to exchange temperature.

Imagine you dipped that spoon into the coffee and then pulled it out moments later before the heat could transfer, and yet the coffee and spoon are exactly the same temperature. What’s going on?

Alan H. Guth. Credit: Betsy Devine (CC BY-SA 3.0)

To address this problem, the cosmologist Alan Guth proposed the idea of cosmic inflation in 1980. That moments after the Big Bang, the entire Universe expanded dramatically.

And by “moments”, I mean that the inflationary period started when the Universe was only 10^-36 seconds old, and ended when the Universe was 10^-32 seconds old.

And by “expanded dramatically”, I mean that it got 10^26 times larger. That’s a 1 followed by 26 zeroes.

Before inflation, the observable Universe was smaller than an atom. After inflation, it was about 0.88 millimeters. Today, those regions have been stretched 93 billion light-years apart.

This concept of inflation was further developed by cosmologists Andrei Linde, Paul Steinhardt, Andy Albrecht and others.

Inflation resolved some of the shortcomings of the Big Bang Theory.

The first is known as the flatness problem. The most sensitive satellites we have today measure the Universe as flat. Not like a piece-of-paper-flat, but flat in the sense that parallel lines will remain parallel forever as they travel through the Universe. Under the original Big Bang cosmology, you would expect the curvature of the Universe to grow with time.

The horizon problem in Big Bang cosmology. How is it that distant parts of the universe possess such similar physical properties? Credit: Addison Wesley.

The second is the horizon problem. And this is the problem I mentioned above, that two regions of the Universe shouldn’t have been able to see each other and interact long enough to be the same temperature.

The third is the monopole problem. According to the original Big Bang theory, there should be a vast number of heavy, stable “monopoles”, or a magnetic particle with only a single pole. Inflation diluted the number of monopoles in the Universe so don’t detect them today.

Although the cosmic microwave background radiation appears mostly even across the sky, there could still be evidence of that inflationary period baked into it.

The Big Bang and primordial gravitational waves. Credit: bicepkeck.org

In order to do this, astronomers have been focusing on searching for primordial gravitational waves. These are different from the gravitational waves generated through the collision of massive objects. Primordial gravitational waves are the echoes from that inflationary period which should be theoretically detectable through the polarization, or orientation, of light in the cosmic microwave background radiation.

A collaboration of scientists used an instrument known as the Background Imaging of Cosmic Extragalactic Polarization (or BICEP2) to search for this polarization, and in 2014, they announced that maybe, just maybe, they had detected it, proving the theory of cosmic inflation was correct.

Unfortunately, another team working with the space-based Planck telescope posted evidence that the fluctuations they saw could be fully explained by intervening dust in the Milky Way.

Planck’s view of its nine frequencies. Credit: ESA and the Planck Collaboration

The problem is that BICEP2 and Planck are designed to search for different frequencies. In order to really get to the bottom of this question, more searches need to be done, scanning a series of overlapping frequencies. And that’s in the works now.

BICEP2 and Planck and the newly developed South Pole Telescope as well as some observatories in Chile are all scanning the skies at different frequencies at the same time. Distortion from various types of foreground objects, like dust or radiation should be brighter or dimmer in the different frequencies, while the light from the cosmic microwave background radiation should remain constant throughout.

There are more telescopes, searching more wavelengths of light, searching more of the sky. We could know the answer to this question with more certainty shortly.

One of the most interesting implications of cosmic inflation, if proven, is that our Universe is actually just one in a vast multiverse. While the Universe was undergoing that dramatic expansion, it could have created bubbles of spacetime that spawned other universes, with different laws of physics.

Multiverse Theory — Artist concept of the multiverse. Credit: Florida State University

In fact, the father of inflation, Alan Guth, said, “It’s hard to build models of inflation that don’t lead to a multiverse.”

And so, if inflation does eventually get confirmed, then we’ll have a whole multiverse to search for in the cosmic microwave background radiation.

The Big Bang was one of the greatest theories in the history of science. Although it did have a few problems, cosmic inflation was developed to address them. Although there have been a few false starts, astronomers are now performing a sensitive enough search that they might find evidence of this amazing inflationary period. And then it’ll be Nobel Prizes all around.

April 30, 2017May 1, 2017 by Bob King

Star-travel 5 Million Years Into The Milky Way’s Future

Two Million Stars on the Move

Gaze into Gaia’s crystal ball and you will see the future. This video shows the motion of 2,057,050 stars in the coming 5 million years from the Tycho-Gaia Astrometric Solution sample, part of the first data release of European Space Agency’s Gaia mission.

Gaia is a space observatory parked at the L2 Lagrange Point, a stable place in space a million miles behind Earth as viewed from the Sun. Its mission is astrometry: measuring the precise positions, distances and motion of 1 billion astronomical objects (primarily stars) to create a three-dimensional map of the Milky Way galaxy. Gaia’s radial velocity measurements — the motion of stars toward or away from us — will provide astronomers with a stereoscopic and moving-parts picture of about 1% of the galaxy’s stars.

Think about how slowly stars move from the human perspective. Generations of people have lived and died since the days of ancient Greece and yet the constellations outlines and naked eye stars appear nearly identical today as they did then. Only a few stars — Arcturus, Sirius, Aldebaran — have moved enough for a sharp-eyed observer of yore to perceive their motion.

Given enough time, stars do change position, distorting the outlines of the their constellations. This view shows the sky looking north in 91,000 A.D. Both Lyra and the Big Dipper are clearly bent out of shape! Created with Stellarium

We know that stars are constantly on the move around the galactic center. The Sun and stars in its vicinity orbit the core at some half-million miles an hour, but nearly all are so far away that their apparent motion has barely moved the needle over the time span of civilization as we know it.

This video shows more than 2 million stars from the TGAS sample, with the addition of 24,320 bright stars from the Hipparcos Catalogue that weren’t included in Gaia’s first data release back in September 2016. The video starts from the positions of stars as measured by Gaia between 2014 and 2015, and shows how these positions are expected to evolve in the future, based on the stars’ proper motions or direction of travel across space.

This frame will help you get your footing as you watch the video. Orion (at right) and the Alpha Persei stellar association and Pleiades (at left) are shown. Credit: ESA/Gaia/DPAC

Watching the show

The frames in the video are separated by 750 years, and the overall sequence covers 5 million years. The dark stripes visible in the early frames reflect the way Gaia scans the sky (in strips) and the early, less complete database. The artifacts are gradually washed out as stars move across the sky.

Using the map above to get oriented, it’s fun to watch Orion change across the millennia. Betelgeuse departs the constellation heading north fairly quickly, but Orion’s Belt hangs in there for nearly 2 million years even if it soon develops sag! The Pleiades drift together to the left and off frame and then reappear at right.

Stars seem to move with a wide range of velocities in the video, with stars in the galactic plane moving quite slow and faster ones speeding across the view. This is a perspective effect: most of the stars we see in the plane are much farther from us, and thus seem to be moving slower than the nearby stars, which are visible across the entire sky.

Artist’s impression of The Milky Way Galaxy to provide context for the video. The Sun and solar system are located in the flat plane of the galaxy, so when we look into the Milky Way (either toward the center or toward the edge), the stars pile up across the light years to form a band in the sky. If we could rise above the disk and see the galaxy from the halo, we’d be able to look down (or up) and see the galaxy as a disk with winding spiral arms. Credit: NASA

Some of the stars that appear to zip in and out of view quickly are passing close to the Sun. But motion of those that trace arcs from one side of the sky to the other while passing close to the galactic poles (top and bottom of the frame) as they speed up and slow down, is spurious. These stars move with a constant velocity through space.

Stars located in the Milky Way’s halo, a roughly spherical structure centered on the galaxy’s spiral disk, also appear to move quite fast because they slice through the galactic plane with respect to the Sun. In reality, halo stars move very slowly with respect to the center of the galaxy.

Early in the the visualization, we see clouds of interstellar gas and dust that occupy vast spaces within the galaxy and block the view of more distant suns. That these dark clouds seem to disappear over time is also a spurious effect.

After a few million years, the plane of the Milky Way appears to have shifted towards the right as a consequence of the motion of the Sun with respect to that of nearby stars in the Milky Way. Regions that are depleted of stars in the video will not appear that way to future stargazers but will instead be replenished by stars not currently sampled by Gaia. So yes, there are a few things to keep in mind while watching these positional data converted into stellar motions, but the overall picture is an accurate one.

I find the video as mesmerizing as watching fireflies on a June night. The stars seem alive. Enjoy your ride in the time machine!

April 18, 2017April 14, 2020 by Fraser Cain

Do I Believe in UFOs?

Whenever I do a new livestream on Instagram (hint hint, @universetoday on Instagram), it’s generally with an audience that doesn’t have a lot of experience with my work here on Universe Today or YouTube.

They’re enthusiastic about space, but they haven’t been exposed to a lot of the modern ideas about astrobiology and the search for extraterrestrials. They have, however, seen a lot of TV and movies.

March 24, 2017April 4, 2017 by Bob King

Watch Stars Orbit The Milky Way’s Supermassive Black Hole

Stars circle 'round the Milky Way central supermassive black hole. Credit: ESO

The Milky Way’s supermassive black hole, called Sagittarius A* (or Sgr A*), is arrowed in the image made of the innermost galactic center in X-ray light by NASA’s **Chandra Observatory**. To the left or east of Sgr A* is Sgr A East, a large cloud that may be the remnant of a supernova. Centered on Sgr A* is a spiral shaped group of gas streamers that might be falling onto the hole. Credit: NASA/CXC/MIT/Frederick K. Baganoff et al.

When your ordinary citizen learns there’s a supermassive black hole with a mass of 4 million suns sucking on its teeth in the center of the Milky Way galaxy, they might kindly ask exactly how astronomers know this. A perfectly legitimate question. You can tell them that the laws of physics guarantee their existence or that people have been thinking about black holes since 1783. That year, English clergyman John Michell proposed the idea of “dark stars” so massive and gravitationally powerful they could imprison their own light.

This time-lapse movie in infrared light shows how stars in the central light-year of the Milky Way have moved over a period of 14 years. The yellow mark at the image center represents the location of Sgr A*, site of an unseen supermassive black hole.
Credit: A. Eckart (U. Koeln) & R. Genzel (MPE-Garching), SHARP I, NTT, La Silla Obs., ESO

Michell wasn’t making wild assumptions but taking the idea of gravity to a logical conclusion. Of course, he had no way to prove his assertion. But we do. Astronomers now routinely find bot stellar mass black holes — remnants of the collapse of gas-guzzling supergiant stars — and the supermassive variety in the cores of galaxies that result from multiple black hole mergers over grand intervals of time.

Some of the galactic variety contain hundreds of thousands to billions of solar masses, all of it so to speak “flushed down the toilet” and unavailable to fashion new planets and stars. Famed physicist Stephen Hawking has shown that black holes evaporate over time, returning their energy to the knowable universe from whence they came, though no evidence of the process has yet been found.

On September 14, 2013, astronomers caught the largest X-ray flare ever detected from Sgr A*, the supermassive black hole at the center of the Milky Way, using NASA’s Chandra X-ray Observatory. This event was 400 times brighter than the usual X-ray output from the source and was possibly caused when Sgr A*’s strong gravity tore apart an asteroid in its neighborhood, heating the debris to X-ray-emitting temperatures before slurping down the remains.The inset shows the giant flare. Credit: NASA

So how do we really know a massive, dark object broods at the center of our sparkling Milky Way? Astronomers use radio, X-ray and infrared telescopes to peer into its starry heart and see gas clouds and stars whirling about the center at high rates of speed. Based on those speeds they can calculate the mass of what’s doing the pulling.

The Hubble Space Telescope took this photo of the 5000-light-year-long jet of radiation ejected from the active galaxy M87’s supermassive black hole, which is aboutt 1,000 times more massive than the Milky Way’s black hole. Although black holes are dark, matter whirling into their maws at high speed is heated to high temperature, creating a bright disk of material and jets of radiation. Credit: NASA/The Hubble Heritage Team (STScI/AURA)

In the case of the galaxy M87 located 53.5 million light years away in the Virgo Cluster, those speeds tell us that something with a mass of 3.6 billion suns is concentrated in a space smaller than our Solar System. Oh, and it emits no light! Nothing fits the evidence better than a black hole because nothing that massive can exist in so small a space without collapsing in upon itself to form a black hole. It’s just physics, something that Mr. Scott on Star Trek regularly reminded a panicky Captain Kirk.

So it is with the Milky Way, only our black hole amounts to a piddling 4 million-solar-mass light thief confined within a spherical volume of space some 27 million miles in diameter or just shy of Mercury’s perihelion distance from the Sun. This monster hole resides at the location of Sagittarius A* (pronounced A- star), a bright, compact radio source at galactic center about 26,000 light years away.

Video showing a 14-year-long time lapse of stars orbiting Sgr A*

The time-lapse movie, compiled over 14 years, shows the orbits of several dozen stars within the light year of space centered on Sgr A*. We can clearly see the star moving under the influence of a massive unseen body — the putative supermassive black hole. No observations of Sgr A* in visible light are possible because of multiple veils of interstellar dust that lie across our line of sight. They quench its light to the tune of 25 magnitudes.

Merging black holes (the process look oddly biological!). Credit: SXS

How do these things grow so big in the first place? There are a couple of ideas, but astronomers don’t honestly know for sure. Massive gas clouds around early in the galaxy’s history could have collapsed to form multiple supergiants that evolved into black holes which later then coalesced into one big hole. Or collisions among stars in massive, compact star clusters could have built up stellar giants that evolved into black holes. Later, the clusters sank to the center of the galaxy and merged into a single supermassive black hole.

Whichever you chose, merging of smaller holes may explain its origin.

On a clear spring morning before dawn, you can step out to face the constellation Sagittarius low in the southern sky. When you do, you’re also facing in the direction of our galaxy’s supermassive black hole. Although you cannot see it, does it not still exert a certain tug on your imagination?

February 3, 2017February 10, 2017 by Fraser Cain

Weekly Space Hangout – February 3, 2017: Meredith Rawls & the LSST

Host: Fraser Cain (@fcain)

Special Guest: Meredith Rawls

Meredith is a Postdoctoral Researcher in the Department of Astronomy at the University of Washington. She writes software to prepare for the coming onslaught of data from the Large Synoptic Survey Telescope and studies weird binary stars. She is also the lead organizer of the ComSciCon-Pacific Northwest workshop for STEM graduate students in Seattle this March. Meredith holds degrees in physics and astronomy from Harvey Mudd College, San Diego State University, and New Mexico State University. When she’s not science-ing or telling people all about it, she plays viola, volunteers at summer camp, and advocates for more equity and less light pollution.

Guests:

Paul M. Sutter (pmsutter.com / @PaulMattSutter)
Kimberly Cartier ( KimberlyCartier.org / @AstroKimCartier )

Their stories this week:
Oxygen on the moon

Nearby “super-void” shapes galaxy motion

First science from Keck’s vortex coronograph

We use a tool called Trello to submit and vote on stories we would like to see covered each week, and then Fraser will be selecting the stories from there. Here is the link to the Trello WSH page (http://bit.ly/WSHVote), which you can see without logging in. If you’d like to vote, just create a login and help us decide what to cover!

If you would like to join the Weekly Space Hangout Crew, visit their site here and sign up. They’re a great team who can help you join our online discussions!

If you would like to sign up for the AstronomyCast Solar Eclipse Escape, where you can meet Fraser and Pamela, plus WSH Crew and other fans, visit our site linked above and sign up!

We record the Weekly Space Hangout every Friday at 12:00 pm Pacific / 3:00 pm Eastern. You can watch us live on Universe Today, or the Universe Today YouTube page

October 20, 2016 by Fraser Cain

What is a Nova?

There are times when I really wish astronomers could take their advanced modern knowledge of the cosmos and then go back and rewrite all the terminology so that they make more sense. For example, dark matter and dark energy seem like they’re linked, and maybe they are, but really, they’re just mysteries.

Is dark matter actually matter, or just a different way that gravity works over long distances? Is dark energy really energy, or is it part of the expansion of space itself. Black holes are neither black, nor holes, but that doesn’t stop people from imagining them as dark tunnels to another Universe. Or the Big Bang, which makes you think of an explosion.

Another category that could really use a re-organizing is the term nova, and all the related objects that share that term: nova, supernova, hypernova, meganova, ultranova. Okay, I made those last couple up.

I guess if you go back to the basics, a nova is a star that momentarily brightens up. And a supernova is a star that momentarily brightens up… to death. But the underlying scenario is totally different.

New research shows that some old stars known as white dwarfs might be held up by their rapid spins, and when they slow down, they explode as Type Ia supernovae. Thousands of these "time bombs" could be scattered throughout our Galaxy. In this artist's conception, a supernova explosion is about to obliterate an orbiting Saturn-like planet. Credit: David A. Aguilar (CfA) — In this artist’s conception, a supernova explosion is about to obliterate an orbiting Saturn-like planet. Credit: David A. Aguilar (CfA)

As we’ve mentioned in many articles already, a supernova commonly occurs when a massive star runs out of fuel in its core, implodes, and then detonates with an enormous explosion. There’s another kind of supernova, but we’ll get to that later.

A plain old regular nova, on the other hand, happens when a white dwarf – the dead remnant of a Sun-like star – absorbs a little too much material from a binary companion. This borrowed hydrogen undergoes fusion, which causes it to brighten up significantly, pumping up to 100,000 times more energy off into space.

Imagine a situation where you’ve got two main sequence stars like our Sun orbiting one another in a tight binary system. Over the course of billions of years, one of the stars runs out of fuel in its core, expands as a red giant, and then contracts back down into a white dwarf. It’s dead.

Some time later, the second star dies, and it expands as a red giant. So now you’ve got a red dwarf and a white dwarf in this binary system, orbiting around and around each other, and material is streaming off the red giant and onto the smaller white dwarf.

Illustration of a white dwarf feeding off its companion star Credit: ESO / M. Kornmesser

This material piles up on the surface of the white dwarf forming a cosy blanket of stolen hydrogen. When the surface temperature reaches 20 million kelvin, the hydrogen begins to fuse, as if it was the core of a star. Metaphorically speaking, its skin catches fire. No, wait, even better. Its skin catches fire and then blasts off into space.

Over the course of a few months, the star brightens significantly in the sky. Sometimes a star that required a telescope before suddenly becomes visible with the unaided eye. And then it slowly fades again, back to its original brightness.

Some stars do this on a regular basis, brightening a few times a century. Others must clearly be on a longer cycle, we’ve only seen them do it once.

Astronomers think there are about 40 novae a year across the Milky Way, and we often see them in other galaxies.

The term “nova” was first coined by the Danish astronomer Tycho Brahe in 1572, when he observed a supernova with his telescope. He called it the “nova stella”, or new star, and the name stuck. Other astronomers used the term to describe any star that brightened up in the sky, before they even really understood the causes.

During a nova event, only about 5% of the material gathered on the white dwarf is actually consumed in the flash of fusion. Some is blasted off into space, and some of the byproducts of fusion pile up on its surface.

Tycho's Supernova Remnant. Credit: Spitzer, Chandra and Calar Alto Telescopes. — Tycho’s Supernova Remnant. Credit: Spitzer, Chandra and Calar Alto Telescopes.

Over millions of years, the white dwarf can collect enough material that carbon fusion can occur. At 1.4 times the mass of the Sun, a runaway fusion reaction overtakes the entire white dwarf star, releasing enough energy to detonate it in a matter of seconds.

If a regular nova is a quick flare-up of fusion on the surface of a white dwarf star, then this event is a super nova, where the entire star explodes from a runaway fusion reaction.

You might have guessed, this is known as a Type 1a supernova, and astronomers use these explosions as a way to measure distance in the Universe, because they always explode with the same amount of energy.

Hmm, I guess the terminology isn’t so bad after all: nova is a flare up, and a supernova is a catastrophic flare up to death… that works.

Now you know. A nova occurs when a dead star steals material from a binary companion, and undergoes a momentary return to the good old days of fusion. A Type Ia supernova is that final explosion when a white dwarf has gathered its last meal.

October 6, 2016August 21, 2020 by Fraser Cain

Where Are All The Alien Robots?

If you’ve seen at least one other episode of the Guide to Space, you know I’m obsessed about the Fermi Paradox. This idea that the Universe is big and old, and should be teeming with life. And yet, we have no evidence that it exists out there. We wonder, where are all the aliens?

Ah well, maybe we’re in a cosmic zoo, or maybe the Universe is just too big, or the laws of physics prevent any kind of meaningful travel or communications. Fine. I doubt it, but fine.

September 19, 2016February 22, 2017 by Fraser Cain

Does Our Galaxy Have a Habitable Zone?

I’ve got to say, you are one of the luckiest people I’ve ever met.

For starters, you are the descendant of an incomprehensible number of lifeforms who were successful, and survived long enough to find a partner, procreate, and have an offspring. Billions of years, and you are the result of an unbroken chain of success, surviving through global catastrophe after catastrophe. Nice going.

Not only that, but your lineage happened to be born on a planet, which was in just the right location around just the right kind of star. Not too hot, not too cold, just the right temperature where liquid water, and whatever else was necessary for life to get going. Again, I like your lucky streak.

Yup, you are pretty lucky to call this place home. Credit: NASA

In fact, you happened to be born into a Universe that has the right physical constants, like the force of gravity or the binding force of atoms, so that stars, planets and even the chemistry of life could happen at all.
But there’s another lottery you won, and you probably didn’t even know about it. You happened to be born on an unassuming, mostly harmless planet orbiting a G-type main sequence star in the habitable zone of the Milky Way.

Wait a second, even galaxies have habitable zones? Yep, and you’re in it right now.

The Milky Way is a big place, measuring up to 180,000 light years across. It contains 100 to 400 billion stars spread across this enormous volume.

We’re located about 27,000 light years away from the center of the Milky Way, and tens of thousands of light-years away from the outer rim.

The Milky Way has some really uninhabitable zones. Down near the center of the galaxy, the density of stars is much greater. And these stars are blasting out a combined radiation that would make it much more unlikely for life to evolve.

Radiation is bad for life. But it gets worse. There’s a huge cloud of comets around the Sun known as the Oort Cloud. Some of the greatest catastrophes in history happened when these comets were kicked into a collision course with the Earth by a passing star. Closer to the galactic core, these disruptions would happen much more often.

There’s another dangerous place you don’t want to be: the galaxy’s spiral arms. These are regions of increased density in the galaxy, where star formation is much more common. And newly forming stars blast out dangerous radiation.

Fortunately, we’re far away from the spiral arms, and we orbit the center of the Milky Way in a nice circular orbit, which means we don’t cross these spiral arms very often.

We stay nice and far away from the dangerous parts of the Milky Way, however, we’re still close enough to the action that our Solar System gathered the elements we needed for life.

The first stars in the Universe only had hydrogen, helium and a few other trace elements left over from the Big Bang. But when the largest stars detonated as supernovae, they seeded the surrounding regions with heavier elements like oxygen, carbon, even iron and gold.

Early stars were made almost entirely of hydrogen and helium. Credit: NASA/WMAP Science Team

Our solar nebula was seeded with the heavy elements from many generations of stars, giving us all the raw materials to help set evolution in motion.

If the Solar System was further out, we probably wouldn’t have gotten enough of those heavier elements. So, thanks multiple generations of dead stars.

According to astrobiologists the galactic habitable zone probably starts just outside the galactic bulge – about 13,000 light-years from the center, and ends about halfway out in the disk, 33,000 light-years from the center.

Remember, we’re 27,000 light-years from the center, so just inside that outer edge. Phew.

The Milky Way's habitable zone. Credit: NASA/Caltech — The Milky Way’s habitable zone. Credit: NASA/Caltech

Of course, not all astronomers believe in this Rare Earth hypothesis. In fact, just as we’re finding life on Earth wherever we find water, they believe that life is more robust and resilient. It could still survive and even thrive with more radiation, and less heavier elements.

Furthermore, we’re learning that solar systems might be able to migrate a significant distance from where they formed. Stars that started closer in where there were plenty of heavier elements might have drifted outward to the safer, calmer galactic suburbs, giving life a better chance at getting a foothold.

As always, we’ll need more data, more research to get an answer to this question.

Just when you thought you were already lucky, it turns out you were super duper extra lucky. Right Universe, right lineage, right solar system, right location in the Milky Way. You already won the greatest lottery in existence.

September 16, 2016February 9, 2021 by Fraser Cain

Weekly Space Hangout – Sept 16, 2016: Universe Sandbox

Host: Fraser Cain (@fcain)

Special Guests:
This week’s guests will be the Universe Sandbox Developers Dan Dixon (Project Lead & Creator) and Jenn Seiler (Astrophysicist & Developer).

Guests:

Morgan Rehnberg (MorganRehnberg.com / @MorganRehnberg)
Dave Dickinson (www.astroguyz.com / @astroguyz)
Kimberly Cartier ( KimberlyCartier.org / @AstroKimCartier )
Paul M. Sutter (pmsutter.com / @PaulMattSutter)
Nicole Gugliucci (cosmoquest.org / @noisyastronomer)
Yoav Landsman (@MasaCritit)

Their stories this week:

What’s the deal with Proxima b?

dark matter galaxy

Enterprise nebula

Unexpected gas reservoirs around large stars

Juno’s first pass at Jupiter

Next Week’s Penumbral Eclipse

Two stars, three planets in an unusual system

Overview of OSIRIS-REx after launch

Status of the Israeli Space Program following the SpaceX Static Fire Test “anomaly”

Is Pluto the source of Charon’s red poles?

China launches its second space station

We’ve had an abundance of news stories for the past few months, and not enough time to get to them all. So we are now using a tool called Trello to submit and vote on stories we would like to see covered each week, and then Fraser will be selecting the stories from there. Here is the link to the Trello WSH page (http://bit.ly/WSHVote), which you can see without logging in. If you’d like to vote, just create a login and help us decide what to cover!

We record the Weekly Space Hangout every Friday at 12:00 pm Pacific / 3:00 pm Eastern. You can watch us live on Universe Today, or the Universe Today YouTube page.

September 12, 2016September 17, 2016 by Bob King

The Big Dipper in the Year 92,000

Stellar motions distort the future sky. Map: Bob King, Source: Stellarium

If we could transport Ptolemy, a famous astronomer who lived circa 90 – 168 A.D. in Alexandria, Egypt, he would have noticed the shift in position of Arcturus, Sirius and Aldebaran since his time. Everything else would appear virtually unchanged. — If we could transport **Ptolemy**, a famous astronomer who lived circa 90 – 168 A.D. in Alexandria, Egypt, he would have noticed the shift in position of Arcturus, Sirius and Aldebaran since his time. Everything else would appear virtually unchanged.

You go out and look at the stars year after year and never see any of them get up and walk away from their constellations. Take a time machine back to the days of Plato and Socrates and only careful viewing would reveal that just three of the sky’s naked eye stars had budged: Arcturus, Sirius and Aldebaran. And then only a little. Their motion was discovered by Edmund Halley in 1718 when he compared the stars’ positions then to their positions noted by the ancient Greek astronomers. In all three cases, the stars had moved “above a half a degree more Southerly at this time than the Antients reckoned them.”

NGC 4414 is a spiral galaxy that resembles our own Milky Way. I've drawn in the orbits of several stars. Both disk and halo stars orbit about the center but halo stars describe long elliptical orbits. When they plunge through the disk, if they happen to be relatively nearby as is Arcturus, they'll appear to move relatively quickly across the sky. Credit: NASA/ESA — NGC 4414 is a spiral galaxy that resembles our own Milky Way. I’ve drawn in the orbits of several stars. Both disk and halo stars orbit about the center, but halo stars describe long elliptical orbits that take them well beyond the disk. When a star plunges through the disk, if it happens to be relatively nearby as in the case of Arcturus, the star will appear to move relatively quickly across the sky. Both distance and the type of orbit a star has can affect how fast it moves from our perspective. Credit: NASA/ESA with orbits by the author

Stars are incredibly far away. I could throw light years around like I often do here, but the fact is, you can get a real feel for their distance by noting that during your lifetime, none will appear to move individually. The gems of the night and our sun alike revolve around the center of the galaxy. At our solar system’s distance from the center — 26,000 light years or about halfway from center to edge — it takes the sun about 225 million years to make one revolution around the Milky Way.

That’s a LONG time. The other stars we see on a September night take a similar length of time to orbit. Now divide the average lifetime of some 85 years into that number, and you’ll discover that an average star moves something like .00000038% of its orbit around the galactic center every generation. Phew, that ain’t much! No wonder most stars don’t budge in our lifetime.

This graphic, compiled using SkyMap software created by Chris Marriott, shows the motion of Arcturus over — This graphic, made using SkyMap software created by Chris Marriott, shows the motion of Arcturus over a span of 8,000 years.

Sirius, Aldebaran and Arcturus and several other telescopic stars are close enough that their motion across the sky becomes apparent within the span of recorded history. More powerful telescopes, which expand the scale of the sky, can see a great many stars amble within a human lifetime. Sadly, our eyes alone only work at low power!

Precession of Earth's axis maintains it usual 23.5 degree tilt, but this causes the axis to describe a circle in the sky like a wobbling top. Credit: Wikimedia Commons — Precession of Earth’s axis maintains its usual 23.5 degree tilt, but this causes the axis to describe a circle in the sky like a wobbling top. The photo is an animation that repeats 10 seconds, so hang in there. Credit: Wikimedia Commons

But we needn’t invest billions in building a time machine to zing to the future or past to see how the constellation outlines become distorted by the individual motions of the stars that compose them. We already have one! Just fire up a free sky charting software program like Stellarium and advance the clock. Like most such programs, it defaults to the present, but let’s look ahead. Far ahead.

If we advance 90,000 years into the future, many of the constellations would be unrecognizable. Not only that, but more locally, the precession of Earth’s axis causes the polestar to shift. In 2016, Polaris in the Little Dipper stands at the northernmost point in the sky, but in 90,000 years the brilliant star Vega will occupy the spot. Tugs from the sun and moon on Earth’s equatorial bulge cause its axis to gyrate in a circle over a period of about 26,000 years. Wherever the axis points defines the polestar.

I advanced Stellarium far enough into the future to see how radically the Big Dipper changes shape over time. Notice too that Vega will be the polestar in that distant era. Map: Bob King, Source: Stellarium

Take a look at the Big Dipper. Wow! It’s totally bent out of shape yet still recognizable. The Pointer Stars no longer quite point to Polaris, but with some fudging we might make it work. Vega stands near the pole, and being much closer to us than the rest of Lyra’s stars, has moved considerably farther north, stretching the outline of the constellation as if taffy.

Now let's head backwards in time 92,000 years to 90,000 B.C. The Dipper then was fairly unrecognizable, with both Vega and Arcturus near the pole. Map: Bob King , Source: Stellarium — Now let’s head backwards in time 92,000 years to 90,000 B.C. The Dipper then was fairly unrecognizable, with both Vega and Arcturus near the pole. Map: Bob King , Source: Stellarium

Time goes on. We look up at the night sky in the present moment, but so much came before us and much will come after. Constellations were unrecognizable in the past and will be again in the future. In a fascinating discussion with Michael Kauper of the Minnesota Astronomical Society at a recent star party, he described the amount of space in and between galaxies as so enormous that “we’re almost not here” in comparison. I would add that time is so vast we’re likewise almost not present. Make the most of the moment.