Is there any consensus out there?

[itsawonder]

I am a layman but I am fascinated with the fields of Cosmology and Astronomy and enjoy watching such programs a "Cosmos" "Unfolding Universe", "Cosmic Odyssey" etc. However, one thing I find troubling is the wildly varying estimates that you hear from various "experts" on these programs.<br /><br />For instance, in the last week alone I have heard on one program that the Milky Way contains 100 billion stars. On another I heard that it contains 500 billion stars.<br /><br />One program states there are an estimated 50 billion galaxies in the universe, another states that there are 100 billion galaxies.<br /><br />One program states that the Massive Black Hole at the center of the Milky Way would be the mass of millions of our Sun but is only the size of our solar system. Another states that the Massive Black Hole is the mass of 3 million suns but is compressed down to the size of a "speck" of dust.<br /><br />It seems to me that just these examples show a significant difference in what the "experts" estimate and conversely would significantly effect the estimates for the amount of matter in the Universe.<br /><br />So the question is "Is there any consensus out there?"<br /><br />(Mod: If you feel this should be in "Ask the Astronomer" feel free to move it)

 

[kmarinas86]

<font color="yellow">For instance, in the last week alone I have heard on one program that the Milky Way contains 100 billion stars. On another I heard that it contains 500 billion stars.</font><br /><br />Estimates of the mass of the galaxy in solar masses are often confused with estimates of the number of stars of the galaxy (which is greater because the average star mass is less than that of the sun).<br /><br /><font color="yellow">One program states that the Massive Black Hole at the center of the Milky Way would be the mass of millions of our Sun but is only the size of our solar system. Another states that the Massive Black Hole is the mass of 3 million suns but is compressed down to the size of a "speck" of dust.</font><br /><br />The former refers to the Schwarzchild radius. The latter refers to the hypothetical singularity.<br /><br /><font color="yellow">One program states there are an estimated 50 billion galaxies in the universe, another states that there are 100 billion galaxies. </font><br /><br />Bwhahahahahhahhahahhah!!!<br /><br /><font color="yellow">It seems to me that just these examples show a significant difference in what the "experts" estimate and conversely would significantly effect the estimates for the amount of matter in the Universe.</font><br /><br />Absolutely.<br /><br /><font color="yellow">So the question is "Is there any consensus out there?"</font><br /><br />There is never a true uniformity of opinion. There is always someone who does not have the same view.

 

[michaelmozina]

I think that at least part of the reason there are such wildly varying opinions on these subjects has something to do with the fact that we are constantly learning new things that tend to change our understanding of the universe around us. The Spitzer, Chandra Hubble and other satellite programs are now allowing us to peer into the universe and into our own galaxy in ways that were never before possible. As a result of this technological revolution, we are discovering a greater abundance of stars than we first expected to find. We have also discovered a greater abundance of galaxies as well. I think it's safe to say that there are *at least* hundreds of billions of galaxies in the universe each one containing hundreds of billions of stars. Counting the exact number of stars in the universe is harder than counting all the grains of sand on all the beaches of the world. It's a little tough to be exactly precise at this point in time, and we learn a lot of new things every day. Even the span of a single year can make a huge difference in the numbers that a someone might report.<br /><br />I think that finding a consensus isn't necessarily impossible, but expecting that consensus to remain a stationary target is a wee unrealistic. <br /><br />There will however always be a difference of opinion on topics and there therefore there will always be a *wide* range of options on every astronomy topic IMO. <div class="Discussion_UserSignature"> It seems to be a natural consequence of our points of view to assume that the whole of space is filled with electrons and flying electric ions of all kinds. - Kristian Birkeland </div>

 

[itsawonder]

"Estimates of the mass of the galaxy in solar masses are often confused with estimates of the number of stars of the galaxy (which is greater because the average star mass is less than that of the sun). "<br /><br />I was referring to the "actual" number of stars, not their "mass"<br />

 

[spayss]

Good question. the answer is 'no'.<br /><br />One side issue is that the numbers become meaningless after a while to human perspective. The numbers are so large that they are only just that..numbers and not descriptive of a reality that we can relate to.<br /><br /> One story I like is an astronomer giving a lecture and listed the number of estimated stars in the universe. He wrote the number on the blackboard and purposely left off a zero. Nobody noticed the error until he pointed it out. He had reduced the whole universe by 10 times but it went over everyone's head. If he had added an extra zero, the same would have happened. If someone told you there was 4 trillion or 40 trillion grains of sand in a pile in front of you, could you really know which answer was correct? The problem with determining the number of stars is we don't even know how big the pile is to look at it. We're making educated guesses by measuring what we know but never sure of what we don't know.

 

[CalliArcale]

Well, not to disparage Carl Sagan, but if one of the programs is Cosmos, it is a bit out of date now. That was produced something like twenty-five years ago. I watched it when it was first on; wonderful show. I haven't seen the superdy-dupperdy-new-FX version; having a kid has really messed with my viewing schedule. <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[bonzelite]

the real truth about the universe is that it is really unknown and nobody really understands it. nobody. this includes all people dead and alive. <br /><br />next question...

 

[thepiper]

I agree.

 

[brandbll]

Well, what if they find out when they die? <div class="Discussion_UserSignature"> <p><font size="3">You wanna talk some jive? I'll talk some jive. I'll talk some jive like you've never heard!</font></p> </div>

 

[nexium]

bonzelite may be correct, but many who post here seem to think they understand the Universe in considerable detail. Estimating the number of galaxies in the visable Universe, requires a lot of number crunching of data from very large telescopes using very long exposure time. While TV producers would like a number, people who issue grants generally don't want to pay for a new count. I suspect it is often difficult to tell a class m star a few million light years away from a small galaxy a few billion light years away. Both typically illuminate only one pixtle, marginally.<br />Counting stars in our galaxy is easier, if we count only main sequence stars and red giant stars, but we do need to arrive at a guestimate of what percentage are hidden from view by dust. Adding in proto stars likely only increases the count by about 1%. We confuse the count greatly if we add an estimate of brown dwarfs and the compact stars in our galaxy, as they may total a million times the number we have charted so far. Neil

 

[bonzelite]

<font color="yellow"><br />Well, what if they find out when they die?</font><br /><br />good good point. i overlooked that. at least they ain't telling us about it (yet). <br /><br />

 

[bonzelite]

<font color="yellow"> I suspect it is often difficult to tell a class m star a few million light years away from a small galaxy a few billion light years away. Both typically illuminate only one pixtle, marginally. </font><br /><br />^^^yes, they are counting what they are <i>able to detect at present with the means available.</i> and that is really a metaphor for the whole of cosmological "soft science," as it is only as useful as it's theoretical laws are allowed to be at the time. <br /><br />but we must forge ahead regardless, or we will certainly learn nothing.

 

[doubletruncation]

Keep in mind that in astronomy typically a "good" measurement is only good to a factor of a few at best. We can say that there are 100s of billions of stars in the Milky Way, and feel pretty confident that we've got the number within a factor of ten. Also keep in mind that it is very difficult to determine the structure of our own galaxy, while in some ways it's a lot easier to study distant galaxies. For the Milky Way you've got to contend with dust obscuring half of the thing, and it's very difficult to know the distance to any star in our galaxy without spending a lot of time getting a spectrum. For a distant galaxy, you get a nice view of the full structure of the thing, and if you can figure out the distance to it (variable stars, masers, tully-fisher relation.. or something) then you can treat everything you see in that galaxy as being that same distance from us without introducing much error (though for nearby galaxies like the magellanic clouds you do have to worry about the "depth").<br /><br />That is not to say that we don't know anything with precision. For example, you can measure masses of stars in eclipsing binaries to about a percent, the parallax distances to nearby stars is even better than that, and there is some confidence that we even know the age of the universe to three signicant digits (don't be too surprised if this one changes though since it's built on many different measurements so there is room for systematic error... particularly in the Hubble constant which historically has been declared to be known with much better precision than was warranted). <div class="Discussion_UserSignature"> </div>