Cosmic Distance Ladder: Standard Candles
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- Опубликовано: 11 окт 2024
- Introducing the concept of standard distance candles as tools for measuring cosmic distances. We explain the key methods and difficulties with identifying and calibrating standard candles. We use the spectroscopic parallax method as an example of a standard candle.
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Right now I'm working on other topics (and I'm teaching an intro physics class for the first time) so it will be a while before I can get to that topic, but it would be interesting to do.
So SN201 1fe happened near 21million years ago and Earthlings got to see it. That timing is pretty amazing!
So basically parallax is needed to calculate luminosity? But there are so many variables, like every star has a different brightness for example.. I honestly thought I’d be able to generally wrap my mind around the concepts of calculating space distance, like I can with most things in astronomy, but standard candles just really don’t make sense to me. Even parallax, while I understand the geometry of it, just seems so unverifiable given all the moving pieces at play.
I guess this is one of those things where the mathematical concepts are way beyond me..
will you talk about stellar evolution??? something like protostar to red giant to supernova??
very clear explanation! thank you for sharing :D
Great video. Maybe I lost something, but you don´t say how Luminosities in the H-R diagram have been measured. In order to know the luminosity of a star compared to the Sun, you need to know distance, what it is what you are trying to measure.
There's a previous video in this series (ruclips.net/video/hP-vN_fteiQ/видео.html) where I talk about that. Basically, for nearby stars we can use the parallax method to measure their distance, and then with the measured flux determine the luminosity. So we do this will many nearby stars (the ongoing GAIA mission has improved this a lot) in order to produce and calibrate the HR diagram. Then for star clusters that are too far to use the parallax method, we've now got the tools to use the method described here.
@@PhysicistMichael Thank you very much, great explanation!
But how do we know the luminosity to these standard candles on the first place? Can we get the luminosity based on estimating the energy output of such stars given their elemental composition?
There's a previous video in this series about HR diagrams and how we need to observe enough stars with known distances (primarily using the parallax method of measuring star distances) to find this original pattern of star luminosities. For each kind of standard candle, you need to have observed enough of them with known distances in order to calibrate how luminous they are, and then you can use them in new cases where other methods of measuring distance fail.
at 0:48 - how do you know the intrinsic luminosity of objects ? Isn't all you have is the amount of light that hits your telescope F ? Looking at the chart on the right - could there not be supergiant that fall outside the general band - for instance with +2.0 Colour and low in luminosity, but we mistake it not to be a super-giant ?
+test123ok sorry. i watched the full video and it made sense :)
You’re from New Orleans?
Why would the larger (heavier) companion star shed mass to the smaller dwarf (especially if the dwarf was formed because it shed all of it's outer material).
Isn't gravity increased with mass/density? Shouldn't the white dwarf just get pulled (told to move) toward the lager companion and then explode after they collide and critical mass is reached?
Remember that the white dwarf star is MUCH denser than the companion star. White dwarfs can be around 1-1.4 solar masses but are about the size of the island of Manhattan. Any material that falls into that gravitational well is going to have a heck of a time getting out. On the other hand the companion star (which may or may not have more mass) might be going through a red giant phase, where the core is heating up and causing it's outer layers to expand out right to where the white dwarf is waiting to pull it all in.
thanks :)
Standard candle and standard parallax is same or different?
how do you measure the intrinsic luminosity of any star?
spectral lines
I´m not satisfied.
Okay, what part do you have a problem with?
Michael, your video is awesome, haters are gonna hate. Thanks for the video series I found it extremely useful!