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Astronomers' model sheds light on microlensing event
In order for MACHOs to make up dark matter, they must be so faint that they can't be directly detected. Instead, astronomers looked for a phenomenon known as microlensing. During a microlensing event, a nearby object passes in front of a more distant star. The gravity of the closer object bends light from the star like a lens, magnifying it and causing it to brighten.
Read more at: phys.org...
By studying the LMC, astronomers hoped to see MACHOs within the Milky Way lensing distant LMC stars. The number of microlensing events observed by various teams was smaller than needed to account for dark matter, but much higher than expected from the known population of stars in the Milky Way. This left the origin of the observed events a puzzle and the existence of MACHOs as exotic objects a possibility. "We originally set out to understand the evolution of the interacting LMC and SMC galaxies," explains lead author Gurtina Besla of Columbia University. "We were surprised that, in addition, we could rule out the idea that dark matter is contained in MACHOs." "Instead of MACHOs, a trail of stars removed from the SMC is responsible for the microlensing events," says co-author Avi Loeb of the Harvard-Smithsonian Center for Astrophysics.
Read more at: phys.org...
Originally posted by MystikMushroom
reply to post by XPLodER
I thought stars being used as gravitational lenses was well documented?
Maybe I'm missing something but I try and keep up on the science headlines. When I saw your title I went, "Well, duh of course they are!"
What are these other members claiming?edit on 30-10-2012 by MystikMushroom because: (no reason given)
Originally posted by DerepentLEstranger
reply to post by XPLodER
LL
seems obvious to me
focal length would be proportional to gravity and size of gravitational source.
i was accused of believing that everything we can see outside of our galaxy,
was a gravitational lens,
Originally posted by Phage
reply to post by XPLodER
i was accused of believing that everything we can see outside of our galaxy,
was a gravitational lens,
I think the criticism had more to do with your ideas about the heliosphere having a lensing effect and how that effect makes the whole universe appear smaller than it really is. Sort of like "objects in the lens are farther than they appear".
Gravitational lensing isn't quite that.
Yes, gravitational lensing collects light. This does not make distant objects appear closer, that is not what the distance calculations are based upon.
it is commonly accepted that without gravitational lensing very distant objects would not be "visible' to us and our telescopes, this is predicated on the ability of large masses to collect and focus light from distant sources and "increase" our ability to "see further" and detect them.
Binoculars use very precise alignment and spacing of prisms and lenses to enlarge distant objects. When I use binoculars I do not normally use the view to determine the distance of the objects I am looking at, I use it to make to objects more readily visible. However, knowing the characteristics of the optical system and the actual size of an object I could do so.
an example would be binoculars, using known optical physics we can use the shape and refractive index difference in air and lensing materials to make objects appair "closer" to the observer,
I think you are oversimplifying. The distance of very distant objects is not determined simply by how they appear as a result of gravitational lensing.
add to that the gravitational potential of a single sun and its abiltiy to "bend light" on its path and you have a situation not unlike looking through binoculars "backwards"
what do you think?
Originally posted by DerepentLEstranger
reply to post by XPLodER
well wasn't one of the proofs of relativity the deflection of starlight by the sun?
in addition to proportionality i also meant it would be a function of
perhaps instead of saying individual stars can be gravitational lenses (micro lenses)
it would be more correct/specific to say that it's gravity wells that act as lenses?
Originally posted by Phage
reply to post by XPLodER
Yes, gravitational lensing collects light. This does not make distant objects appear closer, that is not what the distance calculations are based upon.
it is commonly accepted that without gravitational lensing very distant objects would not be "visible' to us and our telescopes, this is predicated on the ability of large masses to collect and focus light from distant sources and "increase" our ability to "see further" and detect them.
Binoculars use very precise alignment and spacing of prisms and lenses to enlarge distant objects. When I use binoculars I do not normally use the view to determine the distance of the objects I am looking at, I use it to make to objects more readily visible. However, knowing the characteristics of the optical system and the actual size of an object I could do so.
an example would be binoculars, using known optical physics we can use the shape and refractive index difference in air and lensing materials to make objects appair "closer" to the observer,
I think you are oversimplifying. The distance of very distant objects is not determined simply by how they appear as a result of gravitational lensing.
add to that the gravitational potential of a single sun and its abiltiy to "bend light" on its path and you have a situation not unlike looking through binoculars "backwards"
what do you think?
edit on 10/30/2012 by Phage because: (no reason given)
they would "appair" to our observation to be smaller and further away.
"objects in the mirror are CLOSER than they appair
what do you think?
Originally posted by Phage
reply to post by XPLodER
they would "appair" to our observation to be smaller and further away.
"objects in the mirror are CLOSER than they appair
what do you think?
The apparent size of astronomical objects is not used to determine their distance.
Originally posted by Phage
reply to post by XPLodER
Brightness is not used to calculate the distance of very distant objects.
Thus, we can observe a Cepheid, note how long it takes for its brightness to vary and plot that information on an already established graph to find out its intrinsic luminosity. Comparing this true brightness (its 'absolute magnitude') with its apparent brightness as seen in the sky (its 'apparent magnitude') allows us to calculate how far away it is, using the inverse-square law of brightness. "Fortunately, Cepheids are luminous enough that they can be observed in other galaxies, not just in our own. In the 1920s Edwin Hubble used the period-luminosity relation for variable stars to establish the distances to various galaxies and proved that they lie far outside our Milky Way.
What makes you thing that would not be considered in the calculations?
i believe that optical and gravitational considerations would "affect" the apparent magnitude and absolute magnitude results
Originally posted by Phage
reply to post by XPLodER
What makes you thing that would not be considered in the calculations?
i believe that optical and gravitational considerations would "affect" the apparent magnitude and absolute magnitude results
And are you ignoring redshift?
A NEW COSMOLOGICAL DISTANCE MEASURE USING AGN
One of the simplest and, perversely, most intractable problems in astronomy has been to discover how far away something is. New distance measures have led to fundamental
changes in our understanding of the Universe; for example
Tycho Brahe’s supernova and Edwin Hubble’s Cepheids radically reshaped our understanding of the cosmos. It is almost
two decades since type Ia supernovae (SNe) were shown to
be accurate standard candles (Phillips 1993). That distance
measure led directly to the discovery of the acceleration of
the Universe and dark energy
Originally posted by kwakakev
It does sound like an interesting project trying to quantify the lensing effect of the heliosphere. Considering how much trouble man had in first hitting the moon, trying to hit a star is in a new order of complexity. If we had a decent telescope on voyager it would give a good frame of reference conclusively to prove how much effect there is, without it we need other methods.
All of the night sky passes through this heliosphere filter, so it is all subject to the same distortions, be that 0 effect, very minor or quite considerable. So trying to define this effect through referencing star relationships has its problems as it is all subject to the same unknown error.
So if we just focus on just one star and go back to your glass sphere analogy, as we move around in side the glass sphere, the distortions to our perception of the outside will change. I am not sure if our telescopes are sensitive enough to measure any such distortions, but when we are closest to the star in our annual orbit any distortions will be at their minimum and more circular in shape. At the points of 3 months before and 3 months after, any distortions will be at our practically measurable maximum with a slight oval shape. Depending how much change there is between these circular and oval shapes over the year will help define how much influence the heliosphere has in our perception of the universe.