Light Years Ahead and Apart

Every day is a learning experience when you’re covering Texas A&M Science. In many cases, that experience doesn’t end with the finished story — for us as the writers or for the reporters who choose to pick it up.

It should come as no surprise that our professors are natural educators, in and outside their classrooms. Email and social media, along with news outlets that enable and encourage reader comments, offer extended opportunities for those savvy enough to harness them in the ever-broadening realm of public education and outreach.

Take, for instance, the recent most-distant-galaxy discovery. Astronomers Casey Papovich, Vithal Tilvi and Nick Suntzeff went to great lengths to help us get that story not only out but also accurate, from handling initial interviews to helping with multiple revisions and small tweaks to the article in progress as well as to the supporting images and captions.

Galaxy_ArtistRendering_TilviBreathtakingly beautiful, isn’t it? But as good as it is and we thought we did, it turns out people — general readers and even some astronomers — got a bit confused regarding the distance part of that most distant galaxy find. Enter the chance to educate, as illustrated in the following two examples.

In the first, Papovich expands on the 30 billion light years question in response to a direct email from a science writer in Germany:

Technically, the answer is “yes,” but I tend to use the distance the galaxy appears to be (that’s where we “see” it) That distance is only 13 billion light years distant.

The 30 billion light years comes from the following. If you could stop the universe expanding and run a tape measure, then the distance we would measure would be 30 billion light years. But we don’t see the galaxy there. I tend to quote the “light travel distance” because that’s the distance the galaxy “appears” to be (the light left the galaxy 13 billion years ago and has been chasing after us as we are carried away with the expansion). That distance (the light travel distance) is 13 billion light years.

 Now, the galaxy we’re seeing has also been moving in the other direction for 13 billion years, so it has also moved away. That’s why the present-day distance is 30 billion light years (but we can’t see the galaxy at that distance). Because we “see” the galaxy at the light travel distance, I quote that distance (13 billion light years).

Distances are very screwy because the universe is expanding so fast.

Hope that helps, Casey

And here’s the second example, in which Suntzeff responds to a comment on the story featured in the local newspaper, The Bryan-College Station Eagle:

The attentive Eagle readers here have caught an obvious mistake, but let me turn this into a learning moment (hey, give me a break! I am a professor at A&M.) When you measure distances to stuff in the universe, the meaning of distance is ambiguous. It has taken 13 billion years for this light to get to us from this galaxy, and this is one way of measuring distance. Another way, which is often used in astronomy, is asking how much the universe has expanded since that time — sort of how far away is the object in today’s much larger universe. We call this the “scale” distance. That number is more like 30 billion light years for this galaxy. For me, it is easier to think of distance as how long it took the light to get to us, which would be 13 billion years. But the 30 billion year distance is also correct, if not obvious. And yes, this will be on the mid-term.

Any way you slice/write it, I think it’s pretty darned cool we get paid to promote the likes of a discovery of the most distant galaxy known to man (one born only 1 billion years or so after the Big Bang) alongside such great ambassadors for astronomy, Texas A&M University and the state of Texas, and science education as a whole. Welcome to Aggieland!


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