Podcaster: Richard Drumm
Title: UNAWE Space Scoop – Explosions Help Us Measure Distances in the Universe
Organization: 365 Days Of Astronomy
Link : http://365daysofastronomy.org/ ; https://spacescoop.org/en/scoops/2125/this-one-winged-cosmic-butterfly-holds-a-baby-star/
Description: Space scoop, news for children.
How do astronomers measure extremely large distances in the far away corners of the Universe? So this would be the top step on the cosmic distance ladder.
An international team led by Dr. Maria Dainotti, an Assistant Professor at the NAOJ, the National Astronomical Observatory of Japan, has just found a new way to do it. This is because it is quite hard to find standard candles bright enough to be seen more than 11 billion light-years away from us.
You see, the farther out in space we look, the further back in time we see and the closer we get to seeing the Big Bang, the harder it is to find these objects. At 11 billion light-years away from us, these objects get rarer and rarer.
Bio: Richard Drumm is President of the Charlottesville Astronomical Society and President of 3D – Drumm Digital Design, a video production company with clients such as Kodak, Xerox and GlaxoSmithKline Pharmaceuticals. He was an observer with the UVa Parallax Program at McCormick Observatory in 1981 & 1982. He has found that his greatest passion in life is public outreach astronomy and he pursues it at every opportunity.
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Transcript:
This is the 365 Days of Astronomy Podcast. Today we bring you a new episode in our Space Scoop series. This show is produced in collaboration with Universe Awareness, a program that strives to inspire every child with our wonderful cosmos.
Today’s story is…
Explosions Help Us Measure Distances in the Universe
How do astronomers measure extremely large distances in the far away corners of the Universe?
Measuring distances in the cosmos has been a tricky bit of astronomical business for a long time.
First we used the transits of Venus in front of the Sun to determine the size of Earth’s orbit.
Then we used the size of Earth’s orbit as a baseline for parallax measurements to the closest couple hundred stars.
The usual example of parallax is to hold your thumb up and switch between seeing it with your left and then your right eye.
The position of your thumb seems to shift as you view it from different eyes.
The same thing happens with the close stars, we can photograph them when Earth is on opposite sides of its orbit and measure the shift of the star in relation to other stars.
To measure more distant stars we turned to Cepheid variable stars, and Henrietta Swan Leavitt coined the term “standard candle” to refer to stars of a known intrinsic or absolute brightness.
So standard candles are objects, sometimes stars and sometimes supernova explosions, which have the same absolute brightness, or the brightness you’d see if you were right next to ‘em.
Then, by comparing the object’s absolute brightness to its apparent brightness, or what we can see from Earth, with a simple bit of mathematics we can use the inverse-square law to determine the distance to the star.
And there are a number of different methods that have been used to determine distances in the Universe, some good up close and others useful at long distances.
This has come to be called the Cosmic distance ladder, where a series of steps are used to measure distances.
We derive the distances one step at a time!
Where was I… Oh yeah! The original question:
How do astronomers measure extremely large distances in the far away corners of the Universe?
So this would be the top step on the cosmic distance ladder.
An international team led by Dr. Maria Dainotti, an Assistant Professor at the NAOJ, the National Astronomical Observatory of Japan, has just found a new way to do it.
This is because it is quite hard to find standard candles bright enough to be seen more than 11 billion light-years away from us.
You see, the farther out in space we look, the further back in time we see and the closer we get to seeing the Big Bang, the harder it is to find these objects.
At 11 billion light-years away from us, these objects get rarer and rarer.
So Dr. Dainotti’s team started looking for some different standard candles to use.
They found that gamma-ray bursts, or GRBs, large explosions of radiation resulting from the death of massive stars, could come in handy.
These bursts are bright enough, but their brightness depends on the specific features of the explosion.
So, to use them as standard candles, the team analyzed data from 500 GRBs coming from different telescopes.
By studying the patterns of how GRBs brighten and dim over time, the team found 179 of these objects that are very similar and that could potentially have occurred in a similar way.
Looking at the behavior of their light, the team calculated the brightness and distance for each GRB.
Some of the GRBs are close enough to also have other, short-range standard candles near them that we can use to calculate the distance by other means.
Then the more distant GRBs can have their distances locked in. Easy peasy!
Hey, here’s a cool fact!
Gamma-ray bursts are the most energetic and brightest events in the Universe!
After the Big Bang of course…
There are 2 general types of GRBs.
Those where the burst lasts less than 2 seconds and those where it lasts more than 2 seconds.
The initial bright burst is called the prompt phase, which ends abruptly and is followed by a period of afterglow, as the remnants of the star slowly fade away.
The prompt draws our attention, then we study the afterglow.
The Swift X-ray satellite has discovered the existence of a new exciting feature in the afterglow phase: the plateau emission.
The rate of dimming decreases quickly at first, then slows, then dims quickly again.
This slow dimming plateau in the afterglow indicates that there’s an underlying effect.
One that has the same amount of energy present in all those GRBs where the plateau is detected.
Which, at 42%, is almost half of all GRBs.
Thank you for listening to the 365 Days of Astronomy Podcast!
End of podcast:
365 Days of Astronomy
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